The First House. This sounds almost presidential, or prime ministerial does it not? One could certainly do worse in understanding what the first house is.
Like a president, or a prime minister, or a head coach--the first house is all about recognition and leading. Put in a very simple way, it is how a person takes action, and how other people see that person taking action. There is much to be said for the word "identity" here.
So, what is an identity? Well, it is not necessarily what you think of as you. More often, it is what you act on AS you. In other words, it is often easier for people to understand identity through the lens of what they see you taking a stand on, or acting upon. You yourself, though, why, you will be convinced that there is no other thing that could possibly motivate a person! If you keep getting assigned some specific action on a job, you can thank the first house for that.
When very old branches of astrology were first developed, it was the case that most often they looked at the first house and based the rest of the chart off of what that indicated. It was not a bad way to do astrology, but very frequently it lead to interpretations like "Death by bitey lizards" and all other manner of woeful outcomes. If the stars suggest you are going to die by "bitey lizards" what hope do you have?
As astrology changed, the "omen/fate" aspect of intepretation began to change, and so we have the first house understandings we have now. Sometimes the "bitey lizard" vector is higher than others and we might say to a client "There is a good chance you are going to have bitey lizards come after you." However, we recognize the agency of free will moreso in modern astrology.
Here are some first house key words: Identity, Action, Fire, The Head.
Classically, the ruler of this cusp in a "standard chart" was seen to be Aries.