Help I'm drowning

There's poop everywhere.

We've been starting to try potty training this week. It's not going well. Evan won't sit on the potty, he screams for his diapers, he pees on the floor. And this morning, totally unrelated to potty training, he pooped out the side of his diaper and down his legs and then rolled around on the carpet a little before coming to show me. Oh what a lucky girl am I.

Part of the problem here is that I have no idea what I'm doing. I don't know how to potty train a kid. Everything I read says not to push, he'll do it when he's ready, but Evan's almost 3 1/2 and showing no signs of ever getting there. He wants his diapers changed, sure, but that's about the extent of it. His preschool teachers insist that this is our summer and we need to go for it, but no one will tell me how to go about getting him trained.

Evan understands the potty thing, he's interested when we use it, but as far as his own involvement, you can forget it. And I don't know how to get past that. Not to mention the fact that Ev can't or won't tell us when he needs to go. He won't use the sign for potty, and goodness knows we couldn't get him to say it. I don't want to wait much longer to start, but I really don't know what to do next. Help!