Although this question might seem to be trivial, you should clearly understand that your portfolio consists of open positions (stocks you posses). Your Portfolo AND available cash at your brokerage account makes up your Total Capital - major indicator for every investor.

Example: you have 10 000 invested into stocks and plan to invest 5 000 more, your Total Capital is 15 000, and you will receive recommendations based on calculations made considering available cash. Sure, you will be able to adjust this amount at any time. Buying stocks will deduct available cash and selling - increase the amount.