Essentially digital cameras come in 3 flavours each with advantages and disadvantages.
Compact - Major advantage is that they are small and you could easily put one in your pocket. Disadvantge is that they have small sensors ( more prone to noise ) and not as versatile as Bridge cameras or DSLR.
Bridge cameras - All in one jobs that look similar to an SLR but the lens is not interchangeable but they do generally have a large zoom range. May well have a slower ' start up ' time than an SLR. Larger and more versatile than a compact but with smaller sensors than most DSLRs so more prone to noise at higher ISO's.
SLR. The most versatile as the lens choice is huge.
At this stage probably the best I can say is to spend time in the gallery looking at images that interest you and you may like to take yourself. With a lot of images there is some info of the camera used to give an idea of which of the 3 above catagories it fits. For the purposes of this ignore the camera brand, just the catagory.
Which ever of those catagories fits your bill then the absolute best bet is to visit a camera store and try them out in your hand. Some cameras have very small buttons that you may find hard to operate, or ergonomics that do not suit, and that may direct you towards a particular model. At this point you could canvass opinions on your options on the forum. A word to the wise is to check out the Megapixels thread that is currently running before you get caught up in the crazy world of high mp counts.
As to your question on the Pentax 100D then check this review
http://www.dpreview.com/reviews/pentaxk100d/
Don