Baste stitch is to sew two pieces together with longer stitches, and just enough stitches to keep the pieces together. It is used when pinning would not be enough to secure the two fabrics together. This technique is used so you can go back and sew without the fabric shifting around.
Gather- I like to use a long baste style stitch and tug at the bobbin threads. This pulls the fabric together like a shower curtain on a rod.
Hem is to make a finished edge. You usually turn the raw edge over twice and sew the edge of the fold.
Patchwork is to sew two or more fabric pieces together.
Rights Sides Together means to place two pieces of fabric together and the pretty sides are touching.
Seam Allowance is the distance from the raw edge to the stitch line.
Topstitching is a stitch that helps the main fabric stay in place.
I hope these terms and pictures help you!