They are only necessary if you are having a formal wedding, once you are in the church you have to take them off and put them beside the bouquet.
If you are getting married in spring you can choose materials like lace, cotton and silk, if you are getting married in winter you can choose suede or leather.
The length depends on the style of the dress, a glove that covers your hand and your wrist always suites all types of dresses. Gloves to the elbow or above are suitable for a sleeveless dress.
If you decided to have a wedding dress in a pastel colour you can have matching gloves.