Connecting MacBook to WiFi/Home WiFi Security

Hello,

I need assistancance desperatley. My new MacBook Pro won't connect to my WiFi and I can't login. When I turn on the machine, the connection point is not found and I'm not sure how to secure it under my home wifi. I believe someone may have access to this and it scares me.

Also, my leased xfinity gateway is not secured and wifi is being remotely monitored. I had been tinkering with settings and not sure how to secure it again. I tried working with the Admin portal but not sure what's needed in order to secure it. I just want to ensure my home WiFi is private.

Thank you for your help.