When growing plants from seed indoors, you can plant them nearly any time of the year. However, when setting out to plant them outdoors, you need a strategy.
You should find out the date for the last frost in your area and then the number of weeks prior to that date to plant the seed. This is almost always printed on the seed package.
From here, you plant the seed and prepare for growth. A general rule for planting seeds is about six to eight weeks before the last frost date.