I know this sounds ridiculous but DS is my only child and I literally have no clue about potty training 
He is 2 at the moment and will be 3 at the end of November. He's a bright boy and has excellent speech so can communicate effectively.
He knows what the toilet is and what it is for. He will happily sit on the toilet and has had a wee/poo but largely because we sat him on the toilet and he needed to go rather than him saying he needed to go IYSWIM.
Anyway, the other day he spotted some Spiderman underpants and wanted them so I bought them. At home, he put them on and we talked about being a big boy and going to the toilet etc.
Unfortunately, it was a disaster
. After five minutes, I popped into the kitchen and literally a minute later, DS was crying because he'd done a poo. We sorted it and I didn't make a scene just said never mind etc.
Kept reminding him about going to the toilet but literally about ten minutes after I changed him, he weed in his pants
I gave up at that point because he was upset.
Problem is, I now have no idea what to do next? Shall I try pull ups and just encourage him to try the toilet? Nursery would do this as well (he's there full time) or what?
I was thinking of asking nursery for advice but feel a bit stupid 
Any tips /advice would be much appreciated.