Hi there. Please someone can describe to me how to play this game? what's this games rules?

Hello,
reminder, you can always open the rules of a given game when you are on its table by pressing Ctrl+F1, or activating the view detailed game rules button on the web.

The Fives and Threes rules can be found here.

Hope that helps.

I can't get how does marking points work honestly and would rather someone explain it to me.