A chain can be described simply by having a loop, and then pulling the yarn through the loop to make another loop. A chain of loops.
A magic ring is the start to almost every amigurumi project and is the hardest to learn as a beginner. Watching different techniques on Youtube can help you find what works best for you.
A slip knot is how you make the very first loop on your hook. Always followed by a chain.
The most basic crochet. Put your hook underneath the V shape, grab the yarn and pull it through, and then pull the yarn through both loops on your hook.
An increase is when you put two single crochets in a single stitch. Thus, increasing the amount of stitches in that round.
A decrease is where you begin a single crochet in two stitches before pulling the yarn through. Thus turning two stitches into one, and decreasing the number of stitches in a round.
A half-double crochet is when you wrap the yarn around your hook before inserting into the stitch, and then proceeding like a single crochet.
A double crochet is similar to a single crochet stacked on top of another one. Start like a half double crochet, pull through the first two loops, then pull through the second two loops.
A slip stitch is when you begin a single crochet, but instead pull the first loop straight through the second, flattening the end of a round.
Sewing will change from pattern to pattern. Pin pieces together and sew stitches 1:1.