For the carrier clash, you roll to determine the scenario level as normal (Patrol/Skirmish/War etc.). This provies the upper limit of non-carrier ship you can take in your fleet, but the "carrier"vessel is exempt from this (the "carrier" must, however, be a ship carrying at least 2 flights of auxillary craft).
For example; playing as the Minbari, you roll the dice and end up with a Raid level Carrier Clash. You are entitled to take a Morshin Carrier (Battle) or Sharlin War-cruiser (War) as part of your fleet. Due to the fact that both these ships carry two or more flights of auxillary craft. All the rest of the ships you select for your fleet MUST be of Raid level or below, you may not field a Tinashi War-frigate or Troligan armoured cruiser in this instance (as they are Battle level ships), but could choose from Tigara, Teshlan Ashinta, Leshath, Torotha, etc.
See Sky Full of Stars, Page 166.