I don't have the name of all the helpful sites that can walk you through this, but a great place to start with any crochet questions is the Lion Brand Yarns web site. By googling "crochet" you can also get lots of help.
Important: to begin the joining and to end it, I weave in the yarn forward and backward so it locks, and won't come out. Washing the ghans before giving them away is also a must for me. It's a great way to discover any ends that you may need to secure more tightly...in addition to helping to get rid of any fur or doggie drool from my German shepherds!