Some gardeners prefer to run their leaves through a power mower on a mulch setting to shred them. This may make them more attractive looking and less prone to blowing away. Some people claim it also makes them less likely to get matted, but I'm not sure if this is true. Lacking a power mower, I leave my leaves (ha ha) whole, and they generally work fine. In fact, most trees mulch themselves with whole leaves.
When should you apply your mulch? After a few heavy freezes, which is often about the time the leaves fall. So the easiest, cheapest way to mulch your garden beds would be to simply rake your leaves onto them, and spread them evenly a couple of inches deep, ensuring that the tops of plants aren't covered. Then hope they don't blow away before it snows!