Here is some basic information on some types of film photography relating to cameras I use.

I have 35mm, 127, 620 and 120 cameras and a rapid load 35mm.
620 and 120 are "medium format" films. I do not have a large format camera.

These are the comparative spool sizes (all empty of film). The left is a plastic 120 spool, next a metal 620 spool.
120 and 620 are the same size film, just 620 is a slightly smaller spool forcing you to buy Kodak's film at the time
because 120 film wouldn't run through a 620 camera. Notice the much thinner spool top on the metal vs. plastic spool
and the narrower center beam. Originally 120 was on a metal topped, wood column spool.
Once the patent ran out others made 620, or may have made it under license from Kodak all along.
The smallest spool is a 127 film spool. The 35mm canister with film are for comparison.
120 has been in use since 1901.
Here is a loaded spool of 120 next to a 35mm canister. 120 is paper backed and has no canister, the paper keeps light out.
120 film spools across the camera and winds up around the next spool - you don't rewind it, you just unload the exposed
spool and close it with tape (attached to the film end) to keep it tight.

This is the film side of the 120 or 620 product. The film does not go all the way to either end as you need to wind some
paper onto a spool, so the left side (black) of this is the paper-only leader, the right (pinkish) side is film with paper behind it.
You can see the internal tape that holds the film to the paper on the lead side.
Note that 120 has no sprocket holes, you get a much bigger exposure on the medium format film.
The film is pulled by the winding knob on the exposed roll, not moved mechanically with sprockets like 35mm..
The exposed film height is about 22mm on 35mm film and 55mm on 120 film. 35mm is the outer width of the film
including sprocket holes and information printed on the edge of the negative, 60mm is the outer width of 120 including
information printed on the edge of the negative (typically manufacturer, speed, frame number).
This information is not visible until developed so you can't see it in the exposed film above.

This is the paper back of 120 / 620 film. Depending on your camera, the width of the exposure will vary.
The arrows and bars on the left warn you that you are about to be at your first exposure - you actually
have to wind a lot of paper to get to the film and it can be a bit unnerving the first time.
The number on the back corresponds with the back window on the camera so you know what shot you are on.
120 film has either 8, 10 or 12 exposures, thus the staggered numbering.
The sizes correspond to 6x6, 6x7 and 6x9 cm exposures.
220 film is twice the length but has no paper backing except leader and trailer, allowing for the extra length on the same spool.
I have one 120 camera that mechanically keeps track of your exposure with a counter (although it can't count past 12 anyway),
all others use the window on the back so using 220 film I would have to figure out an approximate wind per exposure and guess.
That is how I run 35mm through a 120 camera as well. The counter window must be light sealed for both 35mm or 220.
Note the placement of the three windows, left; middle; right. The Brownie Box camera on the right has no film in it.
The 120 Kodak pocket camera is on shot 3 while the 620 camera in the middle is on 8.
These are the approximate exposure sizes. The left camera is quite a bit taller (or wider) exposure but the height (depth)
of the right camera makes it appear nearly the same size in this picture. The middle camera is 6x6cm, the right camera
is about 6x7 and the left is 6x9.

Since I know people would be curious, this is the front view of the same cameras (with the pocket camera now open):
Left is a 1927 Kodak Pocket camera, 120 film.
Middle is a Brownie (Kodak) Hawkeye Flash built 1949-1961, 620 film (the flash is external and I don't have one)
Right is a Brownie (Kodak) Target Six-20, 620 film. ~1946
All cameras have little view finder windows you look into top down, as with a twin lens reflex.
On the left camera the lens box appears on the front top right (near the lens), but it rotates for landscape or portrait.
The middle camera you can see the top view window in front of the handle and the top lens on the front.
The box camera on the right has two view windows, top or side for landscape or portrait photography, thus the two front top lenses.

As a side note, the left camera used a film you could write on the back. Notice on the left side front, a silver vertical bar near the lens? This is a
stylus. On the back (top of camera in the picture of the back above this picture) is a slide down window and you would literally write your notes on the film back.
This is an example of another take on 35mm film, the auto loading camera. Several companies made similar products.
A bit about film
This Agfa is from the mid 1960's.
Should I send in the registration card?
So far as I can tell the camera was used once. The upper box of film (expires May '68) is empty and there
was a rool of exposed film in the camera (see below) but the lower left box of film contains a roll of film in foil
(expires Aug '68). The flash unit (just above the lower left film box) appears to have never been touched or
used, and all four flash bulbs (mostly hidden under the upper right film box) are intact and the battery is waiting
to be installed. Heck, the camera strap (right of the upper right film box) was never even installed.
I had the exposed roll developed but got nothing back - not uncommon for such old film, background radiation kills it.
The Agfa rapid load system was designed to simplify photography. There are two metal canisters, the left
one in this picture has the tail end of an exposed roll wound into it (the holes say EXP AGFA 100 STOP).
Next you would take the empty canister from the right, move it to the left, and place a new roll in the right side.
Like 35mm plastic canisters, a bit of film would be sticking out the new roll. However, you don't have to load the
film onto a winding spool like 35mm, you simply close the back and begin winding and it feeds into the empty
canister. Like 120, you don't rewind, you simply move the film from one side to the other. Note the sprocket
drive is just to the left of the new film canister (right side of the camera) so film is pushed not pulled into the exposed
canister. This leaves a bit of exposed film hanging out the exposed canister, as above, for the processor to grab.
I believe the copper tabs on the right canister allowed the camera to "read" the speed of the film.
Note the rapid load canister lacks the knob on top since there is no need to rewind. However, you
can not fit standard 35mm canister into a rapid load 35mm camera because of that pesky rewind spool.
It is possible to respool a canister from a cassette. You can see my try here: Respooled RapidLoad