Body language - signalling in conversations

I rarely make eye contact with people in conversations and have only recently realized this. The eye contact I do now is done pretty weirdly since I’m not really sure what to do (and also it is scary).

I’ve read some body language books and was also reading this:

I’m not sure about these parts:

I guess the speaker grants permission to the next speaker by simply making eye contact, but I wonder how the next speaker signaled their intention to speak? It would have to be more than mere eye contact.

Again, what is that signal?