Once you found a breed you like, it's time to find a cat or two for your cattery. Cats can be bought from other players, adopted from the rescue shelter, or found wandering as strays. As a beginner, it is not advisable to get one from the shelter, as these cats often suffer from bad mood (which has all sorts of bad consequences that are better left to more experienced players).
Instead, you are probably best off buying from another player. Prices players charge for their cats vary wildly, and often depend on the specific breed and its popularity (or rarity). Some players will sell gladly to newcomers to help them start their own lines, whereas others are wary of this.
Use the search form to search for your preferred breed, and select the "for sale" option. If your browser supports tabs, open each cat page in a new tab so you can better compare them.
The sale forums (new litters and adult cats for sale) are also a good starting point.