Compression is complicated af...
How many times has that crossed your mind? It's crossed mine at least 467 throughout my journey as a producer.
When you break it down to its core it's actually pretty straightforward.
Compression is automated volume adjustment. You set the parameters with the attack and decay (when compression will start and stop), how much it will be adjusted via the ratio, and lastly when the incoming signal will trigger the volume adjustment aka the threshold.
After you enter your desired settings the compressor just automates that volume adjustment every time the incoming signal passes the threshold.
So why is compression so confusing?
Well... I believe compression is confusing because people look at volume as something that should be set and left. For example if you have a guitar playing at a certain volume, it should be good... right?
Kinda... the overarching volume could be good but compression is volume adjustment at a micro level. Think about the overarching guitar volume being a view at a macro level.
What if you played the guitar notes too long?.. compress some of the tail off.
What if you plucked the guitars too loud and you want to decrease the volume of the beginning of the guitar notes a little bit?.. Suppress the beginning of the guitar notes with compression.
The truth is, using compression can give you a lot of cool practical and creative effects. You could do simple volume adjustment to fix sounds to sit in a mix or do some more creative tricks like running a dry signal on your main channel and then set up a parallel channel strip with another version of the same signal super compressed (compressed in the beginning, continuing until the end of the sound). This is called parallel compression and can give an interesting sonic quality to your sound. Layering a squashed signal and dry signal just sounds cool together when done in small doses.
There are tons of different tricks you can do with compression. Let us know what technics are your favorite in the comments.