you're asking for a simple answer to a rather indepth question it seems..
The Simple answer is, select both nurbs objects and attach surfaces...
But to do it, and make it look right, adn good, you have to make sure all the surfaces have their u and v direction flowing correctly together, and they need to have the same number of spans in which ever direction , u or v, that their going to join on..
Sometimes construction history can cause a problem, another thing to look out for...
REally no simple answer for that question
G