At this time there are about 700-800 Tomb Raider Levels in the Internet. To play them all, the only thing you need is the Tomb Raider Level Player. It is given to you as a free extra with Lara's 5. adventure, Tomb Raider Chronicles.
Most of those levels have a content of about 10, 20,... or sometimes even 100 files or more. Those you have to move to many different directories to make the levels playable. If you want to play another one you have to save all those file to a secure place or otherwise they will be overwritten. If you don't want this to happen you have to build up a full archive of level-files by yourself.
And this is the task the LevelManager is created for. It shall help you manage all those jobs of even just do them. The only thing you have to do anymore: Load a level, install it with a single click and get fully relaxed into a new adventure, together with Lara Croft.
The LevelManager is doing the Installation, is managing all you leveldata, cares about your savegames and even your screenshots are imported automatically, if you just want it.