There are several ways to join paracord. The best way is “the Manny Method”
This is with needle:
If you prefer to see pictures of the method, you can see here: http://www.paracordguild.com/how-to-join-paracord-manny-method/
Another way is to melt the ends:
How to Splice and Join Two Colors of Paracord – Sleeve and Stitch Method
Here are several that show “The Manny Method”