I want organize a free event but in configuration section when I set 0€ I have always the paypal option in frontend and Paypal don't accept 0€ payment. So the users can not signup to my events. Where do I wrong ?

Another thing that I did not understand. If I organize a tournament I must create an event and set a tournament? The user who wants to join must first register at the event and pay them and then join the tournament? So he has to make two records for a single tournament? It seems a bit cumbersome.

Remember: These components are built for LAN parties, not for online tournaments.

When you organize a LAN, users pay for the event, and tournaments are (most often) free, and users can choose which tournaments they want to take part in. So, payment is per EVENT, not per TOURNAMENTS. One paid for an event, you can register for *any* tournament associated with it (as it usually works at LAN parties).

I will look at the free events thing for the next version.

If you want to use this component for online tournaments you might be better off waiting a little while. I am soon to release a new overhauled 1.5 Native version of the tournaments component with many improvements which is much better suited for online tournaments (because it does no longer rely on com_mls_events).