I'm not sure if I understand the question.

You can learn to argue/debate in a positive way as it's normal for friends to have different opinions about things. You can say things like, Yeah that's interesting, but I think that...... or I'm sorry but I have to disagree with you about that.....

Emily - there seems to be a word missing in the question... maybe you wanted to write: Friends have to know how to avoid arguing. (but this is not a question) How can friends avoid arguing? (this is a question) What do friends have to do to avoid arguing? (this is also a question). English speakers usually think that arguing means that people say bad things to each other, but it is possible to argue without saying bad things or hurting someone's feelings. Friends should always respect each other, and they should never forget that their friend is important and should not be hurt.

Emily - there seems to be a word missing in the question... maybe you wanted to write: Friends have to know how to avoid arguing. (but this is not a question) How can friends avoid arguing? (this is a question) What do friends have to do to avoid arguing? (this is also a question). English speakers usually think that arguing means that people say bad things to each other, but it is possible to argue without saying bad things or hurting someone's feelings. Friends should always respect each other, and they should never forget that their friend is important and should not be hurt.