If you have never removed a valve cover, when you reinstall it, be GENTLE with the 11 or 12 10mm bolts that hold it down. Thy will snap if you tighten them too hard. The idea is to squish the gasket, not crush it, so start in the center and work outward in a clockwise fashion. Two to three times around. Grip the ratchet at the head. There are that many bolts for a reason, so snug them down, the gasket will keep the oil in. If the gasket is hard, replace it. It's ~$20 at any parts store and most places stock them. A little dab of RTV in the corners of the "humps" helps seal it.

Good luck! There are more write ups on the web if you need/want more info of illustration to this job. It's not hard to do.