from what i understand the government is buying up troubled assets (TARP) from banks and whatnot to get them off the banks books. in return the government gets equity warrants which allows the government to purchase non-voting shares (which probably may or may not be preferred) in the bank from which it bought the troubled assets.
this really all goes back to how our finance system works. normally a bank has 'x' dollars to lend out. once they lend out the 'x' they package up those loans and sell them to someone else. now the bank has more money to loan out. problem is, no one wanted to by debt anymore since many people have been defaulting on those loans.
here is a basic place to start: http://en.wikipedia.org/wiki/Troubled_Assets_Relief_Program