could you say more? Do you mean mate? you use this in assemblies?
What are you looking to join?
For sketch, you may use Fit Spline.
For parts, you may use combine (add) option
For parts in assembly, you may use join option.
Since your in sketch forum, merge points if they can be merged, if they are offset then your gonna have to use the extend tool, between the extend tool and the trim command Im pretty sure you can join sketches