Which one did you get? Bell back or not?
If you don't use a ridge pole then you need a rope front and back to hold tension between the two poles.
Either way is a correct way, no ridge pole just means one less pole to transport.
Rope,,? Most just uses common Sisal,, some guy's get fancy but a couple spools of cheap 5/16 or 3/8 Sisal or Manila works just fine.