SDTL requires the loader by ModGuy, you set up SDT like normal with the Loader, then set the path to SDT in the SDTL settings.
Got this straight from the front page of the mod:
You should get familiar with using SDT before you start using SDTL. Also, SDTL most likely won't increase SDT's performance for you as it runs SDT at a higher quality than Flash is even capable of.