Joining yarn is an essential crochet skill if you want to make anything that requires more than one skein. Joining yarn is connecting a new skein of yarn to old when you run out of it. If possible, always join yarn at the end of a row or round (it's easier to weave in the ends later on).

To join yarn, snip off the old skein to have a tail of at least 4 inches. DO NOT FINISH OFF. Make a slip knot from the new skein and tighten it around your hook. Pull the old loop over the new loop and tie it taught; then begin a new round. For a color change, it's done in the same manner; if it's more complicated than a simple stripe, your pattern will show you when and how to connect it.

To weave in ends, finish off a swatch or project. You will have at least 2 tails; four if you joined any yarn during the project and possibly more if you changed colors. Thread a tail through a tapestry needle (I'll have a list of all these things for patterns later) and start weaving it through the turning chains of the fabric. Take care to make the weaving as discreet as possible. Repeat this for however many tails you have on the project.

And that's it! I'm going to include a shopping list real quick in the next chapter.