Yesterday I was looking around in the config.yml and I saw "maxconnetions:10". Now I want to know what that means:

Does it mean that only 10 people can connect on the server?
Or can I only save 10 bans?

Please answer my question

It defines the maximum number of active MySQL connections the plugin will open.

And what is that rate ok for many bans? because often the plugin strikes and I saw in the console:
You have reached the maxconnections:10 shutting down plugin.. So as I saw that I have put that to 100.. Is this option ok?

Even for a big server 10 is way enough, so try setting to 5 for example.

What happen If I put there to many connections?

Your MySQL database may either start having performance problems, and/or you'll reach the maximum connection limit it allows, anything else interacting with your database may start to fail.

Ok. And the Performance depents of the GB RAM that the server has got?

This get's a little side-tracked ^^ Such question you may better ask at Spigot or Sponge forums, depending on your Minecraft server software.