A couple of elementary questions from a new user

In general, apps do not need to be closed. If you want to close them, or if your iPad starts to act strange due to low memory, you can close recently used apps in the following manner.

4 finger swipe up the screen to reveal the multitask bar

Long press on any app until a red minus sign appears

Touch the minus sign on any app you want to close (what you are doing here is removing it from memory and forcing it to start from the beginning instead of from where it was suspended).

Swipe down the screen to return to normal.

As far as your wifi is concerned, you may find it a bit more reliable if you reboot your router. You could check Settings/Wi-Fi and make sure Ask To Join Networks is turned off. That way, known networks should be joined automatically.