The Seeker's role in a Quidditch match is to catch the Snitch, a tiny golden ball with wings. Catching the Snitch ends the game and earns the respective Seeker's team 150 points.

+seek snitch
   Before catching the Snitch, this command must be used to check that you can see it. Use this command before a pose and include the results within the pose. You may not attempt to +catch until the next round.
(Available in game and practice code)

+catch snitch
   Determines whether or not you may catch the Snitch. You can only use this command once you have seen the Snitch (you have performed a successful +seek). If you are successful, you earn 150 points and the game ends. There are three possible results: You catch the snitch, you fail to catch the snitch but retain sight of it, or you fail to catch the snitch and cannot see it anymore. In the first two cases, you may try to +catch again on the next round. In the third case, you need to successfully +seek again before you can attempt another +catch.
(Available in game and practice code)

In full game mode, as the rounds progress, the code makes it gradually easier to successfully seek and catch the Snitch to ensure the games don't go on forever.

+pursue
   Full game: When Seeker A sees the Snitch, Seeker B has two options:
a) Continue play as normal and try and +seek it themselves.
b) +pursue against Seeker A. In a failed +pursue, they have just used up their turn for the round and must pose trying to keep up with the first Seeker but failing and falling behind. In a successful +pursue, they are considered to be tailing the first Seeker. In this case, no +seek is required, but they must permit the first Seeker to try to +catch before they attempt to do so.
Use this command before you pose and include the results within your pose.
   Practice: The code works the same, but you must specify who you are pursuing - the syntax becomes +pursue [name].

If you are hit with a bludger:
Grazed: Miss one turn.
Hit hard: Miss two turns. If you are currently chasing the Snitch, you lose sight of it. If you are currently tailing another Seeker, you are knocked off course and must start over again from +seek. Three hard hits knocks you off of your broomstick.
Knocked off broom: You are out of the game.

The code automatically assumes everyone is always doing their best to dodge bludgers, so there is no command required to avoid them. The message regarding whether or not you were hit will be emitted to you after your turn.

+dodge
   Using this command will test your abilities to dodge against an oncoming Bludger.
(Practice code only - NOT available during games)

+skip turn
   Use this on your turn if you have been hit with the bludger (two rounds in a row if you are hit hard). The code will not permit you to execute any other commands until your number of missed turns are up.
(Full game only - NOT available during practice)

For your reference...
All three of these are only available to you during games.

+lineup
   During a full game, this command will bring up the player lineup for the two teams that are currently competing. It also lists their positions. If you have ANSI colours turned on, players who are actually connected will have purple names.

+qhelp
   For those players struggling to remember which commands are available to them during a full game, typing this command will bring up a short list of what they can use, along with a short description of the command.

+report
   During a full game, this will bring up a list of statistics for the game in progress. Basically, it gives a report of who has the Quaffle, where the Bludgers are on the field, and who has yet to take a turn, amongst other things.