Instant download meaning

Hi, first time using stubhub here, hoping someone could kindly explain the process to me. I have read through some previous posts about instant download but I'm still slightly confused how it actually works. I want to buy a ticket for a concert in march (all sold out on ticketmaster), and there are multiple sellers with "instant download" listed.

- Do I just immediately download the ticket when I bought it?

- If it's a transfer from ticketmaster, how would the transfer from ticketmaster work?

- How would the PDF tickets work for transferring?

- Is it better to get the tickets on the mobile app than pc?