Anti matter is the counterpart to regular matter except all properties(except mass and spinn) is reversed. So a anti electron has positive charge, a anti proton has negative charge ect.
Each particle has a anti particle but some particles is its own anti particle.
When a particle and its anti particle interacts they get converted into pure energy

Only way to get 100% matter to energy conversion.
http://en.wikipedia.org/wiki/Anti_Matter
If you let 23 grams of antimater interact with regular matter you get a blast equivalent to a one megaton nuke.