There are three passwords that apply: Admin password. This is what you type in when you go to 192.168.1.1 or a similar address, and lets you change settings. Don't share it with anyone, even people who need to access your network.
WPA2 password for your main network. Give this to people you trust well enough to let them access your network and anything shared on it. Probably household devices only. This is not an admin password.
Password for the guest network. Give to anyone you want to have internet access. Could be WPA/WPA2, or it could be a captive portal.
Can you post a screenshot (feel free to blank out anything personal like network names) of the 'unsecured' message and where you enter the password.