...and it looks like a lot of stuff to pick up, and things like my posts (although neither John Huntington nor Dave "The Rat" are exactly comfortable reading in that regard, either) are scaring you.
Like a lot of things, sound is easier than you think to do (and is harder than you think to do well).
It is an Art, a Science, Engineering, and a Craft. Not all of these have the same weight. At the very top, at the most basic, it is about achieving a desired aesthetic effect. In the words of the immortal Duke Ellington, "If it sounds good, it is good."
And, oh, but this is where the part that resembles Science comes in. Because the final measure is your ears. Because even if you've done reams of engineering analysis, applied tons of highly technical test equipments, and so on, the final tweak is by nothing more than your ears and your own sensitivities.
But...and here's the big "but," before you can apply your ears in this way you need to absorb a little piece of the Scientific Method. To wit, to acknowledge Feyman's Dictum, "You are the easiest person for you to fool."
It is this simple; using tools like the double-blind test is what separates an audio professional from the snake-oil salesmen and credulous consumers of certain "audiophile" magazines. All the measurements in the world won't tell you if the system "sounds good," but the best Golden Ears in the industry won't save you if you are only hearing what you want to (or expect to) hear.
That's why we measure, that's why we test, that's why we calculate. That's why a sound person walks around, moves their head, covers one ear. That's why you turn off the microphones every now and then to figure out what is actually in the sound system and what is actually in the room.
What separates the good sound person from every other person in the room with an opinion -- from the producer down to the guitarist's Significant Other -- is that you know not to trust your own impressions blindly. You've learned to test your assumptions.
This happens at every level, in every part of what you do with sound. Don't assume the power is cut off when you are tying in; apply a chicken stick before you apply bare flesh to a 220 bus. Don't assume the mics are where you placed them last night, or the speakers are still working, or the hiss is the air conditioning.
And don't assume your own particularized aesthetic reaction and baggage of associations hold true for every listener. For some people, the mere sound of a dentist's drill gives them the shakes. For one director I worked with, "Do You Believe in Magic" was the most romantic piece of music they knew. I personally don't listen to a lot of pop, and rarely pay attention to lyrics anyhow, but many people will chose a piece of transition music based on the words. Which of us is right? It depends on the audience, the production, the surrounding material. It has to be a conscious choice, in other words -- not the untested assumption that what you like, others like, and for the same reasons you like it.
And, yes, this is true of all art and true of all theatrical arts in particular. Because a Fine Artist can turn up their nose at the philistines who "don't get their intent" but in theater we have a duty to communicate to the audience. They don't need to hear your aesthetic interpretation of what a train really means -- they need to know the 12:04 is pulling into town with the gunmen on board.
And that's it. That's the most important part.
Listen. Test your assumptions. Test your hearing. Educate yourself. Experience as many different sounds and environments as you can, explore how sound is shaped by the environment, and discover how perception is shaped -- including your own.
Learn both what a gunshot really sounds like, and what an audience expects to hear. Personally move a microphone around and hear the changes this causes in the sound it is picking up. Stick your ears close to a musical instrument and hear the very different sounds from different distances and directions. Listen to a room, then look at what an RTA is showing you about the room. Make changes, rinse, repeat.
Understanding acoustics (and electronics, and power distribution, and rigging...) will come. That's the engineering part. If you are contracting for a $20K sound system install in a new building, you'd better be doing some math. But a lot of the gear you will encounter is designed to be operated by musicians and amateurs. Most of it will be installed, existing systems (small theaters, clubs, etc.) They may not work optimally, but they will work, and the engineering aspect of your job is largely confined to asking someone else how to turn the thing on.
In practical terms, 98% of this job is a craft. And it is a lousy craft, in that an absurd amount of what you find out you need to know can't be easily derived from first principles. So forget the underlying science, and largely ignore the engineering. It comes down to, more often than not, memorizing long lists of "SM57 works well on snare, is harsh on vocals (unless you are doing metal)" or "If it looks like a Speakon connector but is blue, it is probably a Powercon connector" or "Tip in, ring out, except on Panasonic -- like the old Ramsa board -- where ring is in and tip is out."
Which also sounds like a heck of a lot to digest. And it is, except no-one knows everything and everyone continues to learn, constantly. The trick is, learn the gear you have to hand. Make choices of established, well-parameterized gear when you purchase (there's a reason there are so many '57s out there; people know what they do and understand their peccadilloes.) Pretty soon you will collect a little box of frequently-used parts and tools.
They aren't optimized, and they won't always work, but where there's no time to be creative or to engineer you reach into the box. 57 on the snare, check (I have two standard positions I reach for all the time). 100hz roll-off and 1.7:1 compression with a 44 ms attack on the wireless mic (my standard starting position in many theaters). Track_04 wind from my second purchased sound effects CD for, well, pretty much everything. (Track_06 is nice for cold drafts, snowy scenes, and the like).
Lastly, and to recap, think like a scientist (always double-checking your assumptions, doing math if you can and where you can, using test instruments if you have them, and otherwise checking to see if what you think is happening is what really is happening).
But act like a musician. You are a performer, whether you are creating canned sound effects or mixing a show from FOH. Your choices are artistic and aesthetic and individual. Mics can be turned on and off from a script, but mixing a show is a performance -- and a good FOH performance adds as much to a show as a good trumpet solo.