What does this mean?
 

I recently emailed a venue about a concert, and after taking my name they emailed back the reservation was complete and 当日、会場にて引き換えとなります。? Can anyone tell me what this means? Does it mean I will pick up the ticket on the day?

exchange your proof of purchase with the ticket on that day at that place, i think

I don't see any mention of "proof of purchase" in the original, but other than that, yeah, that's correct.

Yeah I assumed the proof of purchase part, something needs to be exchanged I think, I don't know what else it could be ><

I would say the printed-out email or some kind of a reservation number given in the email. I'm sure OP knows what it should be.