If statement and dropdown - Help

Hello, I am new to all this stuff right here and I need some help, I have a 2 fields, one is a dropdown with someoptions, lets call it "Type" and in that dropdown I have 3 options A, B and C, now In the other field is just a plain field lest call it "Here", what I want to do is that if the Type says A then Here will be have 0, if it says B then 1 and then C 2. or something like that