By default, the internet has no memory. The protocol websites use to communicate (HTTP) is "stateless." That means every time you click a link or refresh a page, the web server treats you like a brand new visitor it has never met before.
Technical cookies are small text files the server gives your browser (the "sticky note" in the comic). Every time you ask the server for a new page, your browser automatically hands that cookie back to the server. This is how websites keep you logged in, remember your language preferences, and keep items in your shopping cart while you browse.
Unlike tracking cookies (which follow you across different sites to serve ads), technical cookies are strictly necessary just to make the website function properly!