in order to know about web 3.0, you should know what web 2.0 stands for.

and for this, check my answer about web 2.0

in short, in web 3.0, or semantic web, the computer will be able to understand on its own what is the information you have is about, and do things with it according to its meaning.

just think about the ways you can understand the content of a web site you are using; looking at movies and pictures and knowing what u see in them, reading an article and understanding what the subject is, and so on. in the future, your computer will have many of this abilites too.