Can't join party maps. NOOB QUESTION

i realize this is a dumb question but i cant find the answer. im trying to finish the uber trails. i join the persons party but a cant figure out how to enter the map. if anyone could let me know how to enter other people's map that would be very helpful.

After you join the party, you go to their hideout and jump into one of their portals.

will give this a try again last time a visited their hide out there were no portals.

the person might have been expecting you to provide the keys for the run. just a thought