The fifty-millimeter is a standard lens that comes with most camera bodies and can be used for many projects. It's not all that wide, nor all that long. It's great for learning, because both the portraits and the landscapes you create will be acceptable. It allows you to get close enough with minimal distortion. Fifty millimeters are fairly inexpensive and are a good choice for people beginning to explore the art of photography.
Macros are fun to use for abstract photography, too.
This flower was taken with a macro lens. I was just a few inches away. I could get a similar image with a 200mm lens, but would have to stand much farther away. By joining a photography group, you'll meet people who have equipment they wish to sell. If you buy something from someone you see often, chances are that person won't sell you damaged goods.