Stock question for new person getting into Stocks

Say I have 1000$ in cash. I spent it to buy say 500 stocks for 2$ each. Say one day those stocks go down and 10 of them go to 0 and next day back to 100 but I haven't sold them.
Can I sell them at 100$? Or did I just lose those 10 stocks?

So I am trying to get into stocks. I know either I can give an investment account to a broker or else I can open up a trade set up and do it myself.

I know a guy who does finance and was going see if he wanted to team up for some investments. I was going to use cash becuase it's something I already own and I don't want to ow someone else.