You cant create more roids from that page, you can only initialize them on that page, really you should not have initiated your first 3 roids to only crystal, when I played I initiated 1 metal, 1 crystal and 1 eonium, anyway for now, to gain more roids you have 2 options:

1. From the Waves page, you can create asteroid scans, then you can scan nearby sectors for uninitiated roids, (its possible you will need to do some research/construction before you can create asteroid scans)

2. Build astropods and a supporting fleet, and use it to attack other players to steal their roids.

This early into the game you would probably be better off doing some scans, as you wont be able to create much of a fleet with only 3 crystal roids.  Good luck!