How to do taming?

I am sorry to ask this question, but I am new to the game. I made a venomancer (sp. eeks), I just retain the skill for taming at lvl 7. Ok now I already have the wolf but I wanted to tame another pet. I went to a mob and notice that "tamable" icon for that mob. It was green to me. So I tried to tame it but then it said "failed" and it tried to kill me. Now that I have said exactly what I tried, what am I doing wrong? b:thanks