leaders./elite.: To organize clanwars, your chosen members should all have anti-cheat software (PunkBuster for Battlefield, FairPlay (FP) for SoFII, etc...), and atleast one of them must have Fraps on during the clanwar to take screenshots of the results. These screenshots will be posted in the "MATCH RESULTS" section of the site and on the forums.
If you want to challenge a clan, I suggest you go on their forums, fill in the "Clanwar demands" form and post it on their forums in the appropriate section.