There are two basic screens, they can both be used as silk screens with any mesh, the difference is the frame, one is wooden the other is made out of aluminium. Aluminium are more durable, If you are doing a lot of printing then you want a screen that will not warp and maintain tension (this is important). Wooden screens are often a lot cheaper but can lead poor quality printing. I suggest buying aluminium screens as they last longer. Wooden screens tend to warp due to wear and tear + reclaiming, seem to lose tension quicker so not great for multi colour work.
Aluminium screens are a bit more expensive though but always work the investment.