In software terms UX can be a valuable tool in understanding how users interact with and feel about a piece of software.
As with every product there are two core elements to consider, one is the visual appeal and the other is the functionality; do people like the look of it and can they use it, and most importantly was the overall experience a positive one, would they use it again. Software must deliver a good user experience if it is to succeed.
The UX process will seek to establish whether screen layouts are visually pleasing and easy to use, are menus straightforward and navigable, do users find any controls easily and understand how to use them successfully etc.
More generally the process should test whether people can navigate the software successfully without getting lost, can they find everything, can they perform, and complete designated tasks successfully and as expected, is the experience as good as it can be. Any frustrations or points of confusion should be identified and rectified before re-testing.