Category theory for Programmers solutions in csharp and rust. Other languages may follow.
https://bartoszmilewski.com/2014/10/28/category-theory-for-programmers-the-preface/
1.4. A category consists of objects which are connected via morphisms. There are identity morphisms. Other morphisms can compose. (https://ncatlab.org/nlab/show/category). The world wide web is a category with websites as objects connected via links as morphisms. Via dns or ip a website can be identified. Redirects from one adress to another is way of composing links.
1.5. Friendships can not be used to construct an identity morphism (you can't befriend yourself). You can view or get suggested friends of friends according to security settings so composition of morphisms is possible.