You seem to be under the mistaken impression that all that is needed to teach something is to know it, thus ignoring what teachers are taught to do when they get their teaching qualifications.
or a calculator to help you
It would need to be a calculator which gives correct answers, which therefore leaves out some Texas Instruments calcs and almost all e-calcs (welcome to what happens when programmers don't check their Maths first when writing a calculator). The Windows calc in Standard mode says 2+3x4=20. Turns out teachers need to know how to do Maths without a calculator.
If you became any other kind of teacher (English, history, science, etc.) you would need to build up a starter pack of knowledge on the subject
And learn how to teach, just like Maths teachers also have to do (well, not in the U.S., but that's another story).
you can have any skill level that allows you to pass the instructions on how to perform equations to the students
No, you have to have a skill level of being able to teach it to all types of students. If you have to teach students that 1+1=2, and you don't know why 1+1=2, and a student asks you why 1+1=2, what are you going to do then? If teaching was nothing more than passing on facts then we could just give every kid books on the subject and do away with school.
since there are things that we take for granted only advanced math classes will teach you
You got that the wrong way around. What's taken for granted by advanced Maths classes is what you are taught only in lower Maths classes. Welcome to a whole bunch of Professors don't know the correct answer to order of operations problems because they don't teach it and have forgotten the rules ๐