It is up to the players to determine when sessions occur. If your character wants to do something, be it explore a hex, kill a known monster or raid a dungeon, it is up to you to schedule a DM and invite any players you want to come along.
Make sure you give the DM fair warning so that he can make sure he has the appropriate game material ready to go, and of course, is available at the requested time.
If approved by a DM, post the session on the Campaign Calendar. A Calendar Event needs several things listed: The DM, The Expedition Leader, a Goal for the Session (explore Hex 56.73, Clear the Silver Mine, Kill Demon XYZ, etc.) and Party composition that the DM has agreed to, and the agreed upon method of Treasure Division. You can use this Sample Calendar Event as a template. Please use Eastern US Date and Time (mostly because that is the timezone where the current DMs live).
From there, post up on the forums to assemble your stalwart companions. The originator of the post is the Leader for that session and is responsible for relaying party actions to the DM when out of combat. The Leader is also responsible for picking the appropriate number and level of party members for the adventure the DM has prepared. Last minute players may be included at the DM discretion but don’t count on it, especially if they do not fit in with the predetermined level restrictions.
Sessions will be accepted by DMs on a first-come-first-serve basis, but we recommend you use the forums so that everyone is aware of what is transpiring in the game world.