Ok, do you have a manual? Have you turned it on?
You need to familiarize yourself with the basic operations. Without turning it on check that the headstock can slide and lock on the rail, check the quill feed, depth control and lock, check that you can tilt up into drill press mode. While you're at it make sure the casters work properly. You also want to make sure the table and carriage will slide and lock, and the table height and lock mechanisms work.
I assume you turned it on before purchase and know that the motor runs but this is where things can get complicated. You'll see a number of threads on the forum where used machines have problems with the speed changing mechanism. I had that problem on my first Shopsmith, a 1954 Greenie.
What I do at this point is mount the big sanding disk and turn the drive shaft by hand while seeing if the speed dial will turn. If it's not down at the slowest speed you need to get it there, and remember to return it to the slowest speed after each use. But always keep the drive shaft moving while doing that. If it seems frozen or sticky at all then hold up, don't force anything.
If the speed dial mechanism has any problems I'd suggest stopping at this point to do some disassembly and cleaning. You'll want to do that soon anyway, but certainly hold off if there are any problems.
I'm sure others will chime in with advice, wait for everyone to offer what advice they have and choose what to do based on your circumstances.
Also, you may be past the point of turning it on already, previous owners like to turn it on to show you it works, sometimes making existing problems worse. But if it runs already, at least get the speed dial down to the lowest speed and look into cleaning and lubing before continuing.