For a new comer to SQL it shoulds like Siraj has the right idea. He has a concept of down time. I see to many times people just installing and expecting it run forever. Then sweating when things go too far and it would take a long time to fix.
Siraj, one task to keep in mind during the down time is reindexing.
Key maintenance tasks that happen regularly are Backing up Database and logs which do not require down time (just "off hours" for best results)
reindexing which will require down time.
You may occasionally have to do performance tunning.
Don't forget disaster recovery (backup hardware and plans).