I am a newbie, like you can see, and this is my first day "working" here. I already have 14 activity, but i saw it's written that is useless to have more than 1 activity per day. Did i made a mistake? Please help me.
No, you didn't make any mistake. You can post as much as you want. But keep in mind that non constructive posts aren't appreciated.
And tell me, i have 18 posts at the moment, but only 14 activity... That means i won't get anymore activity points this week?
But in next week, i will get 4 activity? Because of number of posts...
You cannot get more than 14 activities in 2 weeks. So yes you will not get any other activity until the next period (which will start next Tuesday). You can check when the next activities periods will start here
https://docs.google.com/spreadsheets/d/12saLhlUoqIdairxzuSPu6EYGrt7FN2lOstO1yDjCEbA/htmlview?pli=1