Index Management

Hi all,

I've been creating indeces for my tables but I'm a bit lost
now. I'd like to know how indeces are managed? Are them
autommaticly chosen for a particular query? We choose the good
ones (maybe through a sql command)?
If I create 10 indeces and then I make some queries, how will
postgres manage the indeces and how to work through the queries?

Best regards,

-- 
Paulo J. Matos : pocm(_at_)rnl.ist.utl.pt
Instituto Superior Tecnico - Lisbon    
Software & Computer Engineering - A.I.- > http://www.rnl.ist.utl.pt/~pocm ---    Yes, God had a deadline...    So, He
wroteit all in Lisp!