can you make ideas for your game before the jam starts? 

i mean like to write the ideas on paper, not to code it before the jam starts lol

sure - the only requirement is that the majority of the game is made during the jam. However, do be aware that there'll be a theme announced at the start of the jam. It is optional, but most people who play and rate your game will judge you based on how well you follow it :)

ok, also why does part of me suggest that the theme will be something with a frozen cave or something