Things to keep in mind here are:
1. When you leave tails make sure it is atleast 6 inches long. This will make it easier for you to thread the yarn needle for weaving in and give you enough length to work with.
2. Weaving in is always done on the wrong side of your work and into the part of your work which is the same color as your tail.
3.Yarn needle is a needle with a big eye and a blunt tip. The best way to thread a yarn is snip a bit of the end to remove any frayed edges and wet it. Some people fold the yarn tip and then thread it. Choose what suits you best.
There are a few ways you can weave in the tails.
Crochet around the tails to weave them in.
2. After you finish your work you can weave in the tails using a yarn needle into the wrong side of your work. You have to weave in for almost 2 inches and then skip a few of the stitches you weaved into and go backwards for an inch or so. Then cut the yarn close to your work. Just take care to weave into the same color.