One common case is Separate Around 1 and Make a Line. This means to go past one person and then turn inward to become the center of a new line. The other dancer, the one who was being walked around, slides outward to become an end of the new line.
For Separate Around 2 and Make a Line, the dancers who separated go a bit further, and turn inward to become the ends of a new line. Note that the number "2" refers only to the "inactive" dancers, the ones who aren't doing the Separate. Other "active" dancers, other dancers doing the Separate who you pass on the way, don't count.
Separate Around 1 and Come Into the Middle means that after the active dancers move between the inactive dancers they keep moving forward into the middle of the square, where they will do another call. The inactive dancers slide back together again.
For Separate Around 2 and Come Into the Middle, the inactive dancers don't need to slide apart. But they will typically move inward temporarily, in the same way as if the other couples were promenading around them.