Bus from Salerno to Amalfi

This should help. I think it is designated by letters.

http://theamalficoast.online/timetables_orari/SITA+Amalfi-Salerno+Amalfi-Sorrento.pdf

Those letters refer to the days-of-week key code at top left of the PDF page. I would just look for a bus with a sign saying destination Amalfi. There won't be too many other options, but you don't want to get on a bus southbound to Paestum by accident.

Do you pay on the bus??

No, buy tickets from the newsstand or tobacco shop that's closest to the bus stop or in the train station.

And make sure you buy a round trip ticket. I don't remember there being a ticket window at Amalfi--it's basically just a bus parking lot/transfer area right near the water.

Are the SITA tickets different from the other bus tickets around Salerno? Need to get to Positano and change at Amalfi. Planning on taking ferry from Positano to Capri and then from Capri to Salerno. Possible, right??
Thanks!