Annuals are defined as a plant that only last one growing season. Plants that are annuals in some hardiness zones are actually able to survive year round in higher zones and thus become perennial plants.
Typical annuals usually have lots of color with blooms that last over a long period of time. Think impatiens, petunias, geraniums, purslane (my favorite hot weather annual pictured in the hanging basket to the left), lantana, gardenias, marigolds, and zennias.
Annuals are easy to start from seed, but it takes a long time to get to the blooming stage. Most gardeners opt to purchase starts from the garden center to get that instant, long-lasting pop of color. Annuals are great for filling in spots between blooming perennials, in hanging baskets, in pots and whimsical containers, and for changing up the colors from year to year in the garden.
If you’re really adventurous, you might try collecting some of the seeds in the fall and save them to plant out in the spring when the weather warms up. Just be prepared to wait a while until they get big enough roots to start supporting blooms. A few annuals reseed themselves which can be a blessing or a curse depending on your outlook and style of garden.