OK the ligs being talked about are mainly the fundiform and suspensory ligaments. Think of them as attaching the pubic bone to the base of the penis (they kind of wrap around the base) the tunicae are the the containing envelopes for the two CC and CS (the bits that grow bigger when you are erect).
So when people talk of stretching the ligs they are talking about trying to make the penis pull out of the body a little further, and when they are talking about stretching the tunica they are talking about lengthening the actual length of the penis.
Jelqing generally effects the tunica but if you jelq toward the floor you are putting strain on the ligs.
Generally people new to PE have a fair amount to be gained by stretching the ligaments so they should concentrate there. LOT may help inform you better as to whether this is the case for you.
As a PE career progresses, lig gains dry up and people start working on the tunica.
This is simplification to a degree but more can be learned by reading anatomy threads and checking out other anatomy sources on the web. It makes a lot of sense to have a good understanding of the anatomy of the penis.