If i reinstall steam will my games be installed still?

Title says all, help please.

Not sure, but just do a backup of game files.

No.

If i do this, will they be able to launch instantly, or will i have to wait for them to install:
Coz it’s not my addons i’m worried about, i just don’t wanna wait for the installations.

if you back it up and put it back in right, yes