The stronger the signal received by your device from a base station (or WLAN access point), the faster and more stable is the Internet connection. If your mobile phone is near an open window or outside, the signal is normally better than inside a building. For a connection using WLAN it is important for a "good signal" that there are as few obstacles as possible (e.g. walls) between the WLAN access point and your device (e.g. tablet).