'Myös' works in the same way as 'also' in English. The meaning of '-kin' depends on where you use it. If you attach it to a noun, the meaning is pretty much the same as when using 'myös' (I am also a journalist = Olen myös journalisti = Olen journalistikin) though using 'myös' sounds better in my opinion. You can also say 'myöskin' and it means the same as 'myös'. When attaching '-kin' to the subject, it gets a bit trickier. If you say 'Olenkin journalisti', it can mean "That's because I'm a journalist', 'I'm actually a journalist' or possibly even a question. I probably missed something, but if you want to say also something..., using 'myös' is generally better.