Moisten a plain white or brown paper towel with clean water. Tap water is usually fine, but use bottled water if your tap water goes through a water softener. The paper should be wet but not dripping.
Fold the paper towel lengthwise then crosswise to make a small square.
Put the seeds on the towel. Tomatoes, peppers, peas, broccoli, beans and squash are all good candidates for indoor germination on paper. Root crops like carrots, potatoes and radishes tend to do better when sowed directly into the soil. Hard seeds like peas and beans can be soaked overnight prior to planting on paper to soften their shells and help them germinate faster.
Place the seeds at least a half-inch apart so that the young roots won't touch each other and get tangled or spread mold when they sprout. Germinate more seeds than you plan to grow in case some seeds are dead, especially if you're germinating old seeds.
Label the plastic bag with the date and the type of seed you will put inside it.
Gently roll the paper towel up so that the seeds are folded inside and can't fall out. Place the paper towel inside the labeled plastic bag. Seal the bag halfway to make sure the seeds get enough air but don't dry out too quickly.
Place the bag in a dark place at room temperature. The seeds will not germinate in direct sunlight or in very warm or cold places.
Check the paper once or twice a day to make sure it is moist. If it's starting to get dry, dampen it all over with a spray bottle.
Open the paper towel after two days to see whether the seeds have started to germinate. Remove any seeds that have turned black or are covered with white fuzz. This is mold and it means the seeds are dead. If none of them has germinated, replace the towel in the bag and wait two more days.
Plant the seeds that have germinated. Seeds are ready to sow into the soil when you can see the first root coming out of them. Don't touch the delicate root when you pick up the seeds. You might need a pair of tweezers to pick up very small seeds like broccoli without damaging them. Put the seeds with the root facing downward into pots filled with potting mix, or directly into the garden if the weather is warm enough for them.
Give old seeds extra time to germinate because they might be a little slower. If the seeds haven't germinated after a week, they are probably dead and you can throw them away.