Can-someone-explain-the-Max-Risk

Can someone explain the Max Risk % and how it chooses how many shares to trade. I understand how the stop loss would trade. So that if I set it to 10%, the most I should have as a loss would be 10% of the trade dollar amount.

My problem is trying to figure out how it sizes # of shares to trade in the 1st place and how it chooses which assets to trade and also how I can limit # of positions.

Thank you,
Larry