energized

I'm not real new, I've dabbled in stocks here and there, but I still have a lot to learn. One thing I don't get is the decimals. For instance a stock I was looking at had these numbers:

Open: 0.0035 - Close: 0.0029

So did it open at 3/1000 of a cent? And how many shares would that buy you at if you invested $5000. Could someone explain in easy terms what this means. How do you buy stock for fractions of a cent and why would you?

I don't intend to buy it, just trying to learn new things. Thanks