wifi connection lost when I leave home

If I understand your question, your device (e.g. your phone) is connected to your wifi signal at home (e.g. wifi signal broadcast from your home router), and when you leave your home, you lose that wifi connection. The wifi signal is limited by strength and distance. If you are connected to your wifi signal at home, as you move farther away from the router, the signal gets weaker and then you lose it because you are out of range. If your phone's wifi is still turned on, it will pick up other wifi signals as you enter the range of the other signals.