Join

Connect lines, arcs, polylines, 3D polylines, Helixes and Splines, as long as they are all contiguous (in other words, they share a common endpoint)
Lines, Arcs - Polylines: select polyline 1st
Lines, Arcs, Polylines - 3D Polylines: select 3D polyline 1st
Lines, Arcs, Polylines, 3D Polylines - Helixes: select Helix 1st
Lines, Arcs, Polylines, 3D Polylines, Helixes - Spline: select Spline 1st



Must select the 

most complex object first