Before you move your plants to their permanent location, you should harden them off. That means gradually acclimating them to the outdoors. They've been protected all of their lives and if you were to just throw them outside without preparing them, they may die and all your hard work would be for naught. Your plants have had pretty constant temperatures and light and a sudden change could have drastic consequences.
Before taking them outside, check their size. If you started your seeds in a flat they are most likely ready for a bigger container. Carefully loosen them from their present home and move them to a bigger one. Now is usually a good time to add some organic fertilizer. Give them a gentle watering and let them get accustomed to their new digs for a couple days. Once you can see that they have adjusted well, it's time to start the hardening off process. To begin, I take mine out for an hour at the warmest part of the afternoon. Make sure they are sheltered from any harsh winds or rains. The next day, extend their time outdoors for an extra half an hour. Keep up this routine until the temperatures outside are ideal for your particular plant. Once the danger of frost is past, it is safe to plant them in your garden.