How do I find the network password if I have logged before?

If you have signed into the network in the past it should be in your Mac's Keychain Access. This application is found in Applications folder > Utilities or search for it using Spotlight.

Open Keychain Access and search for the network name. Open the item in the list by double clicking on it. Tick the box asking to Show Password. You may need to enter your Mac's passcode to reveal the password for the item.

Hi, and Happy New Year.

Ordinary WiFi password is printed on bottom of WiFi router or access point.