That lens lineup should do you just fine. I definitely wouldn't go out and get a new lens unless it's what you really want. Your question is a bit too general to answer in an online post. If you're pretty new to photography, your best bet is to pick up a good book like Understanding Exposure. But otherwise, just have fun with it. If you don't have a decent understanding of aperture, shutter speed and ISO, I'd stick with the automatic modes of the camera. The manual and priority (i.e. AV & TV) modes are probable just going to frustrate you if you don't understand what they're doing. That's definitely a goal to work towards, and you can certainly try them out, but it's not worth coming back home with a bunch of terrible pictures if you can't figure them out.
If you're planning on doing landscapes (or really any outdoor pictures), try to get out there within about an hour of sunset or sunrise when the light is nice and soft. That can often be the difference between an OK picture and a great picture. Of course, the there isn't as much light, so you'll generally want a tripod, since the camera will usually have to use a shutter speed that's too slow for you to hand hold the camera steady enough.