You'll need to read up on the details and decide. It depends on how many users and how you want to host your database.
Using just FileMaker PRo, not server, you can host a database that up to 9 other computers using their own copies of FIleMaker Pro can access at the same time (each needs their own license or you get a volumne license). If you enable web publishing, you can also support up to 5 simultaneous connections from users with web browsers.
I suggest that you also pull up the product info on Server and FileMaker Pro before deciding.