The US government is a behemoth, even at its smallest. This is no surprise to anyone who has read the Constitution: simply enacting all of its requirements entails a fairly substantial civil service and body of elected representatives. The interactions of the federal and state governments are controlled by the personalities involved, but also by a vast body of law, some of it harking back to the Constitution and other elements of it established since then - in the form of precedent, case law, amendments, state law, executive orders, and much more. Vast bureaucracies handle issues such as interstate travel, defending American borders, preventing and solving federal crimes, ensuring aviation safety and other functions. Meanwhile all the way to the local level, all sorts of positions are held by elected officers, from county clerks to school boards to mayors.
Knowing how all of this works is the job of the American president. However, as events have shown, you don't have to actually know all of it; if you don't mind blustering your way through four years in office, you can just pretend you know what you're doing and a surprisingly large number of people will buy it. Could you pull that off? Let's find out!