Typically you pin perpendicular to where your seam is going to be with the pins right in the seam line. There are differing opinions but I sew right over the top of my pins. I usually slow down just a bit when I get to the pin but the stitching will (usually

) go right over the pin. Then you unpin after it is all sewn up.
Some things fit and lay together nicely (for example, 2 squares of quilting cotton) and don't usually need a lot pins to keep them in place. Things that are gathered or curved usually need more pins to hold them together while you sew.
Congratulations to you and your daughter. Just keep at it! If you can find a class or know someone that sews, that can be really helpful. But doing it is how you learn and everyone started right where you are so have fun!