Quickest way to play on ICC is to play in the AutoPairing Pools by clicking for example the 3-minute, 5-minute or 15-minute button on top right of Board. This will ask to be paired in that pool and a 15-minute game has a 15-minute rating.
The challenge based system, which tournaments use too, allows direct match requests and seeks. To post a seek to the seek graph, go to Board's Option button - Find a Game on menu. The left tab on top of Find a Game will switch it from seeking to seek graph. Green is regular chess with a human on Seek Graph and solid is rated and hollow is unrated. Blue is computers. Other colors are variants or loadgame. To rematch the last opponent go to Actions button then on menu, rematch.
In seeking, if a new player, use formula on will do nothing, as new users don't have one. If unsure when seeking or not getting responses, seek with formula off or type in console help formula.
If it's not a rematch the only way to directly challenge a friend is to type match username time inc r/u. I.e. match rookers 5 0 r, for a rated game or match rookers 5 0 u, for an unrated.
To Withdraw ones seeks, challenges, and pool requests, the Find a Game option, Pool tab, withdraw challenges, can be used.