If you have large seeds like peas, beans and corn left over from last year, an easy way to test for their viability is to fill a shallow pan with water and pour the seeds in. If they sink, they're fine. If they float, toss them.
If you're starting seeds indoors and not sure how soon to start them in your area, When To Start Seeds should help. How to Successfully Start Plants from Seed will help you do it successfully.
