It needs something to twine around, so you should have a trellis or something similar in place for it before planting which is tall and wide enough to take all its growth.

Yes, it is difficult to impossible to put in a trellis after a vine has been established. Much easier to put the trellis in before you plant it. You could simply put in a single inch-thick stake, but I would cut shallow notches in it to help the twining stems to get a grip.

i'm sorry, I just noticed you mention it growing up a pergola, not sure if that mention was there initially. If your pergola is constructed of thick wooden posts, you will need to put some kind of supports there for the plant to twine round - whether that's wires and eyelets, or thin trellising, or whatever. If the posts supporting it aren't more than 1 inch square , then the plant will twine round it eventually.