The first 4 tier ships you can get for free just buy doing the grind. You can buy the CD to get a quicker start, but play through the tiers until you get the hang of it. Divisions or solo, there are many different play styles available.
The CD contains premium ships that give you extra bonus and credits. But just try it our for free to see if you like it. Its not a quicky shoot em up. you will die fast unless you work with a team usually 4 groups of 3. More like a domination of map center or 3 caps. don't hide behind a rock or your team will lose, get out there and fight!