Where do I find the Raid Calendar? At the top of every page via the "Raid Calendar" link. Once someone adds you to a new event, a small notice icon appears next to it until you have opened that event at least once.
Overview & filters The calendar overview shows all upcoming events. The search box finds events by title, organizer or player name (wildcard * supported). Filters let you hide past events or everything except your own guild's events.
Creating an event Guild masters and officers can do this for their own guild; admins can additionally create board-wide events. Everyone can have at most 4 upcoming events created at once - only once one has passed or been deleted can you create another.
Guild raids are automatically locked to the creator's own faction (Alliance players will not see Horde raids and vice versa). Board-wide events are visible to everyone and open for self-signup regardless of faction.
Signing up On the event page you choose your status: Accepted, Tentative, Bench or Declined. You also pick which class and specialization you are bringing (handy if you are joining on a twink) and can optionally enter a different character name. Your role (Tank/Healer/Melee/Ranged) is pre-filled automatically based on your specialization, but can always be changed manually.
Two rules apply: you can be signed up as Tentative for at most 10 events at once, and you cannot be firmly Accepted for two overlapping events at the same time.
For raid leaders and guild management - Clicking a name in the roster lets you change that person's status, class, specialization and role. - "Add player" lets you sign someone up directly from the guild roster or by username - they automatically get a private message with a link to the event, unless they have disabled that in their settings. - "Send invite" (guild events only) lets you send an invite PM to several guild members at once without signing them up directly. - If you use a softres.it reservation list, signups can be imported from it. - Adding or inviting someone always respects that event's faction (for board-wide events, the organizer's own faction is used) and the target's personal settings.
Your own notification settings Under User Control Panel -> Preferences -> Edit global settings, you can choose whether to receive calendar invite PMs, and whether raid leaders/guild management may add you to events directly without asking first. Both are enabled by default.