Sorry for answering in English, I can't speak Portuguese (but I understand what you write as I know a little Portuguese and it's very similar to Spanish, so that you could answer in Portuguese if you want)
How to do this: First you have to add the other one to your friends.
You can do this by right-clicking (on Mac: Hold down the ctrl-key and click) on a client and selecting 'Add to friend list
Now he will appear at your friend list after clicking in the messages-section of aMule. There you can right-click your friend and select 'Establish Friend Slot'.
This will make aMule create a special upload for this person. The one who messaged you asked you to enable the friend upload and offered you to enable a friend upload to you in return.
Advantage: Both get a upload from each other.
abraço
