On a floor with relatively large tiles the 'cement" in tiling I belive they call it "thin set" can be used without any problems. Make sure the floor is sturdy if it has much movement at all the tiles will work loose. Adhesives work very well for smaller and wall tiles normally not necessary on a floor. Buy the thin set mix for floor tile in the tile area of the store, This will ensure the proper mix of sand cement and so on. Then follow the package instructions as some methods may vary. Make sure you get the proper notched trowel as well. Their are also plenty of floor adhesives made pre mixed made shur their are insructions on the can for the type and size tile you are laying. The premixed adhesive are a bit pricer but more fool proof. I hope I was of help.
When I have put large tiles down (12" x 12"), I have used thinset cement. You basically mix it with water until you get a thick "cake batter" consitency, and then let it set for 5 minutes prior to use.
Note you will also want to back butter the tiles (apply a thin skim coat of cement on the floor tile itself), in addition to applying the thinset to the floor.
The stuff you saw being laid is called 'self levelling floor compound' over here. Its great for making the floor level ready for tiling, as you know liquid will always find a level, so you pour this mix on your floor, help it along by spreading it about the area and wait for it to level out and dry - its great