Q&A for How to Connect Two Laptops Through a LAN

This depends on the software you're using. If you're already using some communication software like Skype or Discord, you can find the option somewhere in the program. Otherwise, you can use online meeting software like Skype or join.me. Both these and many other communication software have a "screensharing" feature. To guide you in how to screenshare with a specific program, we would need to know which program you are using. They're all different.

Try to install drivers for your operating system for the bluetooth, or the button maybe stuck or broken.

While you could set up an ad-hoc peer-to-peer network between them, the easiest way is to connect them both through the same wireless access point/router and share resources over the network.

For security and privacy reasons. When you connect any machine in a network you can share and access resources available in the network. You may give (or have) access to files, folders, printers and other resources. That's why you have to use a username and a password, they will determine the privileges associated with your profile.