Once you make a character, he/she will be of the particular class he/she has chosen. The race/class cannot be changed. Each class has its unique abilities and is played differently than others. Each class is interesting in its own way, which makes playing CF a unique experience with every class. If you wish to play some other race/class, you can create another character, though I do not recommend having multiple characters existing at the same time, as it tends to be time-consuming. CF isn't the easiest of games, but the world is well made, the RP is deep (as it is enforced) and the classes are interesting. But do roll up and try! I haven't played Achaea, so I can't really tell how simple it is to compare.

However, roll up to the fields and learn it yourself! You will be a non-PK character during the first 10 levels, after which you can PK be PK:ed by the people who are in your PK range. The range consists of those characters who have about 30% more experience than you at maximum and the other way around, so the range has more and less experienced characters than you are (feel free to correct me if my figures are wrong, Imms).