Because there are so enormously many different fly patterns, you can make almost anything. Here you can find a few examples that wil give you skills for these and lots of other patterns. See these models as templates for your own creations, to fit your fishing and your fishing places.
The purpose with fly tying is to make copies and visions of the food that the fish prefer to eat. What that is we will see if we search the stomach of a caught (and dead) fisk. Some fly tyers make detailed imitations others make flies that might look as it is something eatable for the fish, even if it sometimes is difficult to see what it should imitate. What the fish think about it, we don't know, but now and then it takes our stuff, so probably the fish think that it is something it can eat. Or they just give it a go. If it's no good they just spit it out again.