A very good way to begin your self-instruction is to read some of the very good Tutorials; most of these are written for the average user, and there are many that cover computer security as well as the use of some of the well-known applications. Remember than an educated user is the best defence against malware infections.
For quick "how-to's" check the mini guides forum.
Changing the oil for computers means some form of scheduled maintenance, the frequency depending on your usage. You could do worse than look at the "slow computer checklist" to get some insight on some of the maintenance activities:http://www.bleepingcomputer.com/forums/t/44690/slow-computer/
Naturally, don't hesitate to post---even if you think the subject is elementary---a question or about a problem you are having. All of us here are users, and began knowing almost nothing about computers ourselves.
Welcome to BC!