Hey there. I use a different brand of dSLR but will try to help speaking in general terms. You are wise to hang out here if you want to learn more about using your camera. (And there are some very knowledgeable Pentax people here as well.)
Low light and/or movement require a "fast" lens. Fast lenses are those that have wide apertures (low f numbers), such as f/1.8 or f/2.8, etc. Most kit lenses only go to f/3.5-4.6 (zoomed) or so, so those might not work great in low light. Fast lenses can be expensive but are worth having as part of a versatile set up that will ultimately help you get the kinds of shots you're after (ie really good ones, lol). They come in different focal lengths so it's good to figure out your style of shooting. (From what I've seen, most people starting off with a dSLR get the kits but realize they need a fast lens or two after using the camera for a while and becoming frustrated their shots are still blurry.) Many people pick up a 50mm f/1.8 to start. This should be a good portrait lens and I believe it's usually reasonably priced.
As for a "multi-use" lens, some refer to that as a "walkaround lens" and it covers a wide variety of focal lengths, for instance 18-180mm. Most will tell you that these types of lenses aren't as good quality as lenses that only cover smaller ranges of focal lengths, but some feel it's worth it for the convenience. For a while I used an 18-180 and truthfully, I didn't see a difference in quality and for me, it was better to use that than to keep switching back and forth between the 14-54 and the 50-150, which I didn't really enjoy doing. (I've since pretty much abandoned it - well, actually, gave it to my son for his beginning set up - after buying some fast lenses which are the only lenses I use now.) But again, if you rely only on this type of lens, you might have difficulty getting low light or action shots.
A couple of suggestions. You mentioned you don't use the camera much. Use it more. The only way to get better is to practice and see what works and what doesn't. Don't just give up on it. If you haven't read Understanding Exposure yet, pick up a copy and read it. It will help you understand the Exposure Triangle (ISO, aperture and shutter speed) which will be the first step toward all of this making sense.
I'm sure others will chime in, but let us know if you have more questions.