What's the Difference Between 'Machen' and 'Tun'?

Both of machen and tun can mean "to do" in English, but they are also used in many idiomatic German expressions that are best learned as vocabulary. Depending on how it is used, 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. 

Even Germans have difficulty explaining the difference between these two words. Of the two, 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.


Their Origins and a few Relatives 

If it isn't obvious yet, machen should remind you of make while tun resembles to do. The brothers Grimm meant that tun had a wider meaning than machen. It is interesting to take a look at a few members of their word families:

Machen

     der Macher: Walter war ein Macher.the doer: Walter was a doer.

     machbar: Ja, das ist machbar.doable: Yes, that's doable.

     anmachen / ausmachen: Mach mal bitte das Licht an.turn on / turn off: Please         turn the light on.

Tun 

• der Täter: Das Opfer kannte den Täter.
  the culprit: The victim knew the culprit. 

• die Tat: Jeden Tag eine gute Tat.
  the deed: Everyday a good deed. 
• sich auftun: Er sah in einen gähnenden (=yawning) Abgrund.
  to gape: He saw into a gaping abyss.  
• etwas abtun: Er tat meine Idee einfach so ab.to reject sth: He simply rejected my idea.

One "Rule"

There's one "rule" that I can give you at hand: whenever you are talking about (not) creating something, you can only use "make":

• Hast du das selbstgemacht? Have you made that on your own?
• Ich habe meine Hausaufgaben nicht gemacht. I haven't done my homework.

But most of the time you will simply wonder which of the two verbs to use. Therefore in the following, you'll find a few useful examples for each verb.

machen		Was machst du da? What are you doing? Was machen Sie von Beruf? What do you do for a living? Das macht nichts. It doesn't matter./Forget it. Wann sollen wir das machen? When are we supposed to do that? Mach's gut! So long!/Take it easy! Das macht... hungrig/durstig/müde/fit. That makes you... hungry/thirsty/tired/fit. Da ist nichts zu machen Nothing can be done (about it). Das macht 10 Euro. That comes to 10 euro. Drei und vier macht sieben. Three and four equals seven.
tun		Es tut mir leid. I'm sorry. Sie tut nichts als meckern. All she does is complain. 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 da mit dem Hammer? What are you doing there with the hammer? So etwas tut man nicht. That's just not done./That isn't a proper thing to do.