Both verbs can mean "do" in English, but they are also used in many idiomatic ways. The verb machen can mean do, equal, give, last, make, matter, take and several other things in English. The verb tun is also used in colloquial German for "put": Tun Sie bitte die Bücher aufs Regal. (Please put the books on the shelf.) The verb machen is more frequently used, so it is best to simply learn expressions that use tun and avoid using that verb if you aren't sure about it. Sometimes they may seem interchangeable (Was soll ich nur machen/tun? = So what am I supposed to do?), but in many cases there are subtle differences that prevent that. Es tut mir leid. I'm sorry. Ich habe nichts damit zu tun. I have nothing to do with it./It's not my concern. Wir tun nur so. We're just pretending. Was tust du mit dem Stift ? What are you doing with the pen? So etwas tut man nicht. That's just not done./That isn't a proper thing to do.