You just need one to print. There are a lot to choose from unless you printed comes with a proprietary one already. If it comes with one, that's all you need. You just import the model (usually an .stl), adjust your settings and print.

If you want to build a model, that takes a separate program. However, Meshmixer allows you some pretty interesting model building controls as well as printing functions.

But, back to your original question, it only takes one program to print, start to end. The choice you have to make though is, which one to use?