Day trading question from a new trader

I am new to trading with margin. I used to have a cash account and I am a little messed up with the day trades left since I have an account smaller than 25k.
When I buy a stock, and I add to my position then I sell its counted as 2 day trades or just 1? How many times can I add to my position? what about shortselling?

Thank you very much and I apologize if this is a really stupid question,
Julio de la Cruz
Hi Julio - welcome to the forum.

What you are talking about is called pattern day trading.

Here are some topics that cover this:

Question regarding Day Trading in Scottrade

Suspended for Day Trading