“Search Engine Optimisation”. The name itself tells you that you are making your content (all the material on your website: text, videos, images etc) into an optimal format and organisation so that it can be found easily by search engines, i.e. machines.
This may lead you to embark on this optimisation process by thinking about the mechanics of the machines. You might start asking questions like: How do the search engines operate? What do they look for? How shall I make it possible for them to find my content?
These are good questions and it helps to answer them but not first because the search engine is being used by a person.
Search engine optimisation means making sure that a search engine places your website high up in its results when a person searches for a particular search term.