BaseElements comes as a set of three fmp12 files. You need to copy the 3 BaseElements .fmp12 files to a location on your hard drive.
BaseElements will let you import as many different solutions into a single copy as you prefer. However some developers like to keep multiple copies of BaseElements, one for each project or client, and this is perfectly fine within the licence agreement. In this way you can keep a single archive of each project's development.
You can also use FileMaker server, although you can only have one copy on each FileMaker Server at any one time.