Blinded creatures are unable to see. This gives them a 50% miss chance and a -4 penalty to all attack rolls, while giving those attacking them a +2 bonus to attack rolls. Furthermore, a blind creature is considered flat-footed and is unable to directly target distant creatures with spells or attacks. Additionally, there is a -4 penalty to discipline, hide, move silently, open lock, parry, pick pocket, set trap and tumble.
True seeing negates most of the effects of being blind, leaving only the 50% miss chance. Similarly, blind fight negates some of the effects of being blind, leaving only the -4 penalty to attack rolls, the -4 penalty to skills, and the inability to target creatures at a distance.
The -4 penalty to attack rolls is for attacking an unseen character. It is not applied multiple times for other instances of not being able to see the target (e.g. if the target is invisible).