A good place to start is how wide you want your ring to be from edge to edge. This is most often measured in millimeters. Just for reference, a "typical" wedding band is usually 3 - 5 mm. If you're not sure, measure out some strips of paper and wrap them around your finger for a visual aid!
While rings often sport a "high polish", there are a number of other options for treating the metal surface. Any polish or texture will change with normal wear, as virtually all precious metals are malleable, We call it "developing a patina", which is just a fancy way of saying the character of any surface treatment is likely to change over time. Very pronounced finishes such as hammer and florentine are more resistant to wear.
The profile of a band is basically a cross section, as if you took a slice out of the ring. As we get more specific, the outside profile of a band refers to the shape of the outside surface of the ring. This is most commonly flat or rounded, but there are lots of other options.
You probably never gave much thought to the shape of a ring's inside surface, also called the inside profile. This is important because it effects the weight (or "heft") of your ring (a rounded inside will mean the ring is heavier than if the inside is flat), but can also play a part in how comfortable it is to wear. Half round and knife edge bands are thinner at the edge, and those styles, as well as very wide bands, will often feel better on your hand if the inside is round instead of flat. Keep in mind that the extra weight will result in a more expensive ring.
There's a lot to see, so, take your time, look around, and learn all there is to know about your options. You will see an approximate price when you have completed the basic choices. Protip: once you have made the basic choices in the designer, your band will open in a new tab with lots of additional info. You can go back to the design page and configure as many designs as you like, leaving the tabs open for easy comparison. Later on we can think about adding things like custom engraving or setting stones.