Two years ago I did my 2 car garage with a kit from Rustoleum... It was from Home Depot for $99 / up to 500sq ft.
It came with the cleaner ( a bio safe orange type ) 2 cans of epoxy paint; gals , 2 cans of epxoy hardener; pints, and two bags of paint flakes to throw on after applied.
First was the floor test... if painted , with a sheet-rock knife cut an X about 4 inches each leg...put duc tape on.. if it pulled up the paint , it had to be cleaned off first... if the paint stayed, it was ok to paint over.
Second, loose cement, crumbling cement had to be fixed.. wire brush out loose, patch.
Third, Cleaner... mix up bio orange cleaner and apply to floor scubbibng with floor broom...rinse with water.
When dry on goes the epoxy... mixed half at a time , best if between 75-85f, more than 60f...higer temp = less working time.
Rolled on a 4x4 sq ft area, throw on flakes, move on...
I started at 9 am and by dark I was able to walk on it ( about 80f), next day moved my stuff back in.
So far, nothing has pulled up, I have some small patches where the paint chipped off ( half-dollar size) but this was due to dropping tools to the floor ... The concret chipped out, not the paint.
Over all... best $100 spend on the garage
Tom
ps... they have a clear overcoat you can also buy for extra... IMHO, not worth it. Also in sneakers it can be a little slippery if wet ( you may want to buy and add some paint sand)