This is my first game jam, so i'm a bit confused on when to start do i start now or in 5 days??

in 5 days when the theme is revealed

Then jam starts, ( in 5 days) there will be posted Theme, which says what type of game you have to create, if you check previous jams, you will find theme, and how people created game, based on theme

Id say have the basics of each genre down, controllers for each genre you are into create, 2D platformer, FPS , TPS.