Mulch has many purposes. It helps minimize weed growth. It slows down water evaporation and adds nutrients to the soil as it decomposes. Mulch maintains more consistent soil temperatures and helps prevent the soil from becoming too compact and from eroding. Leaves make an excellent source for mulching and since leaves are readily available from your own landscape, from a neighbor who might gladly let you take his leaves and even from a local municipal leaf collection site.
Layer leaves around the base of your vegetable plants, about 2 to 3 inches deep. If desired, mow the leaves first so they'll decompose faster and add nutrients more quickly to your soil. A mower with a bag attached will eliminate the need for raking if using chopped leaves.
Place 2 to 3 inch layer of whole leaves in between the rows in your vegetable garden to create a pathway that helps prevent weeds and does not get muddy.
Replace the leaves as needed to maintain a height of 2 to 3 inches throughout the growing season since the leaves will decompose.