The sheets of decals or stickers you see on sale in the markets, which are they?

are they stickers you just stick on or decals that need to be applied wet?

If the latter soapy water is best?

They are just stick ons. many shops selling them in China town.

You mean these? They are to make your race bike go faster

They are stickers, if you get a sticker bigger than 1 square foot and have a curved surface its easier to cut them smaller and rejoin when you apply them.

You can use soapy water to move it around during application but you have to wait for it to dry. You can remove air bubbles by poking it with a needle and heating it up with a lighter, before smoothing it over with a rag.