When we built the new house first thing I did was paint the garage floors.
Used the Rust Oleum Epoxy.
They sell a kit that comes with cleaner, 2 part water based paint and the decorative chips. $65 and will do 250 sq feet or basically 1 garage.
Rust-Oleum Two Part Gray Semi-Gloss Epoxy Garage Floor Coating Kit - 203005 at The Home Depot
But don't buy that. I went this route
Buy it in bulk. They sell the same stuff in gallon containers that's self priming. $30 bucks a gallon that will do 300-400 sq ft.
Rust-Oleum Rust-Oleum 1 Gallon Battleship Gray 1-Part Epoxy Concrete Floor Paint - 181461 at The Home Depot
New floor should not really need a real cleaning, maybe scrub with some simple green just to make sure it's degreased well. You can buy an etcher if you really want for another $10-12 but was not necessary on my new floors.
If you like the chips they sell them separate as well. I opted to not use them since the make it harder to find that stupid little screw, washer, widget that you dropped.
Basically if you buy everything that comes in the kit separately it'll still be less than the kit and cover nearly twice as much.
I used 2.5 gallons to cover a 3 car garage with two coats.
Stuff dries quick as snot to so 2 coats is doable in one day.