Hi L.,
I can only tell you what worked with my son (and as we've all heard before, every child is different)...
My son didn't "know" how to go either -- certainly he could go, just didn't understand what was really happening, etc. So, we just potty trained and he figured it out right quick! I scheduled out 3 days at home -- NO trips anywhere for 3 days, not even the store and put him in underwear, explaining that underpants need to stay dry and that from now on he was to pee and poop in the potty. We also made sure to stay in a part of the house with hard floors (no carpet!) Well, it took him a good day just to even realize that he was peeing, but he eventually got it. He also had a couple of poopy accidents over the next week, but then got that one down, too. At age 2 1/2, I had LOTS of people on this forum tell me that he was "too young" and "not ready" because he never requested to go to the potty, etc. -- well, they were wrong and I sort of wish I'd done it sooner. By the end of 3 days, I felt confident to take him out and now just turned 3, I consider him fully trained and he rarely has an accident unless we are somewhere that he can't use the potty and he really has to go, etc. (and then it is only a few drops in his underwear). Oh, and my son ALSO had fits about sitting on the potty prior to trying. I got tired of being careful not to "push him" and just became his mother -- just not accepting his tantrum, staying CALM and not making an issue of it myself, yet not letting him call the shots. Being very matter of fact about the whole thing helps a lot and always telling (over and over) that "wet underpants are no good".
Anyway, my recommendation would be to go ahead and put him in underwear, stay home a couple of days, and see how it goes. Give it a couple of days and try not to get too frustrated on day one. Keep an open mind -- if he doesn't show ANY signs of "getting it" by the end of day two, I would continue to put it on hold and try again in a couple of months. :-)
Good Luck!!