in addiiton to what ic-said
you probably want to mark off the aspect ratio of your roll film adapter on the ground glass
some use pencil on the glass, i never do, i use clear xerox film / copy shop acetate with a grid xeroxed on it.
cut it to size, and mark off where your roll back sits on it.
you can also make a mask, cut thin paper to fit ontop of your ground glass so it is a grid ..
like you would do with the xerox film, put it against your roll film adapter and mark off the opening so you can
compose on the ground glass. both the mask and grid make composing much easer than guesstimating.
if the camera is on a tripod focus on the ground glass, as you always would, depress the spring brackets and slide off the ground glass
and put the film holder in its place. if it is the speed graphic you are using, look for "view finder masks" they made a bunch of them.
they are numbered, you can poke around graflex.org in the accessories area, i am sure the numbers are easily found on eBoo.
the masks are for viewing 6x6, 6x7, 6x8, & 6x9 they slide infront of your view finder ( not your rangefinder )
you can "zone focus" ... attach the roll film adapter to the back of the camera, set your focus, f-stop, shutter,
and look through the viewer and take your photographs.
using a roll adapter is great with a speed/crown graphic because if you barrel lenses &c you can use it with
any film you want, not just 4x5. and with a view camera you can do perspective control/camera movements with non 4x5 film, it comes in handy.
i used to use a 35mm roll film ( recommar 35 kodachrome ) adapter with my speeder and view camera and graflex slr. it was nice to be able to use a 120 year old lens with roll films and
not deal with sheet film.
of course your mileage may vary.
good luck !
john