Regular wedding bands and engagement rings are very different from each other and it is important to understand what role each piece plays. Tradition is as follows: Wedding bands are the same as wedding rings and are worn by both the groom and the bride. An engagement ring is worn by only the bride. The bride is supposed to wear her wedding band under her engagement ring (closest to her heart). The bride is also able to not wear a wedding band if she chooses not to.
The difference between a wedding band and an engagement ring is obvious. The engagement ring is much more elaborate and extravagant, containing an array of stones, most commonly white/colorless stones such as diamonds, and most commonly one large center stone. A wedding band that can be worn by both the bride and groom does not traditionally have a large stone in the center and is usually much more understated. The engagement ring is generally much more expensive than the wedding band and is presented during the proposal. The wedding bands are exchanged during the wedding ceremony.
While these are the traditional standards concerning wedding bands vs. engagement rings, there is no reason that couples must stick to them. Some people prefer a flashier wedding band featuring diamonds, while some brides prefer their engagement ring to not have stones. Your wedding jewelry is about symbolizing your love and commitment to one another, and your ring choices can be as unique as your relationship.