Litestep replaces the shell that windows comes with (explorer) with a new, better one (Litestep).
all of your windows apps, games, and other things should still work with Litestep. Yes you can change your themes when you like, and if your sure of what your doing you can also change the way your system operates and make it do some new things. Litestep can be changed almost endlessly to suit the user. ONE VERY IMPORTANT THING, MAKE SURE YOU READ THE README'S, AND I STRONGLY SUGGEST YOU GO AND READ THE DOCUMMENTS ON LITESTEP. Then you will find most if not all of your questions answered. But if you have a question that you can't find in the doc's, ask it, don't be afraid to ask. Here is the adress for the doc's page http://lsfaq.shellfront.org/
go there and read what you can, it will greatly help you in the end.