Dear Homebilly,
In case you're still interested, I'll break it down step by step here. Andrea put it very nice and simply (who better), but if you want anymore insight, here you go.
In case you hadn't heard, ExsManager is really great!
The immediate and easiest function of EM is called "relink". You can use this simply by indicating which folder your EXS instruments are in and which folder your samples are in, then clicking [Re-link]. EM will then read each instrument, scan your samples folder to find all samples associated with each one, then write the location of those samples to the EXS instrument itself. This way, when you load the instrument in Logic, it has written into it the locations of all samples referenced by it, and it loads without having to search for the samples.
Without this data written to the EXS instrument, Logic searches all hard drives connected to your system to find the samples, a process which takes WAY too long. If you've opened an instrument once in Logic, however, it does preserve this information, and you won't experience these wait times. You will experience these wait times a) the first time you load an instrument, b) if you've moved your samples, c) if you've re-loaded your instruments (replacing them with copies which do not have the info on locations of samples written into them).
Additionally, EM is great for organizing/reorganizing your library, and can be used to locate redundant samples on your drives, etc. One KEY function is called Sample Merge. This function reads an instrument, then makes a new file that merges together a copy of all samples associated with that instrument. It then makes a new EXS instrument as well, which references locations in the merged audio file, rather than dozens of individual samples. This is very helpful because Logic has a limit to the number of samples that it can reference at one time (somewhere around 11,000), and the VSL performance instruments have around 2000 samples each!!! THis means when you've got 6 performance instruments loaded, you've loaded more samples than Logic can keep track of. With sample-merged instruments, you're much less likely to run into this situation.
So, if that doesn't clear it up, perhaps another of the many patient and helpful users on this forum will give it another go. Stick in there mate, you'll get it.
Best,
P.S. It's far and away worth the money. For me it made the VSL usable, becuase it was just too heavy for my computer (G4). On a G5 now, but I'd still die without EM.