When starting your garden, ask yourself "When is my last spring frost date?" Depending on the area that you live and garden in, you will have you own LSF. For me, it is between April 7 (earliest) to April 23 (latest). Knowing this date allows you to "time" out your vegetable gardening activities.
Next, when can I plant outdoors relative to the LSF? Depending on what you are growing, this can be anywhere from 8 weeks before the LSF to several weeks after the LSF. It also depends if you are direct sowing in the garden or using transplants. (Buying plants may take the guess work out for newer gardeners. Most garden centers and seed catalogs will have plants available at the appropriate time for your area.)
What if you wish to start your own indoors to be transplanted into the garden? Again, you would have to know when you can transplant outdoors according to the LSF? In addition, how long does it take the seedling to reach transplant size? Once you know this, you can figure out when to start your seeds indoors. For example, tomatoes take 6-8 weeks to reach transplant size. They can be planted outdoors 1-2 weeks after the LSF. Counting back (6-8 weeks) from the outdoor planting date, you have your indoor start date!
So remember, before you can go any farther, first determine the average date of your last spring frost for your area. Take the time in January to decide on what it is you wish to grow and how, order seeds, and start "timing" know for a successful start!
"If you have a garden and a library, you have everything you need." --- Cicero