In prison, there are the basics of classic prison (i.e ranking up, mining, etc.). In prison you try and be the best of the best with rare items you can get from looting. Looting is a unique mechanic in which you loot chests and there are chances of you getting special rare-items that have special abilities that are worth a lot. There are prizes for whoever is on the leaderboards at the end of each map, which lasts around ~8 months.
Theres a guide I wrote a few months ago here if you would like to read it: