How do u import base models with ur map

attach base to map or link it to refence frame.

how do i do that

Ive made maps but never had to attach anything to my map in 3DS MAX

I think Pointer might have been thinking of linking, which you do need to know how to do to make a map. Attaching is not neccisary for making a map, but is used alot.
Select you map, go to edit mesh, or edit poly, and click "Attach", then click on your base.

Now they are the same object and you can edit them together. There are tutorials on actually attaching the geometry of the base to that of the map, but long story short, delet the faces of the map around the base, then make new ones from the resulting hole to the base. If you don't know how to do that, you should practice and learn some more about max before trying to do this base thing.

You can also "fuse" them together, but that's more complex. I barely know how it works.

or just read the tutorial that comes with hek.