To add to the previous post about books and core knowledge, here are a few tips to get you started.
You will need to learn things from the surface down and from the bottom back up to the top. By this I mean you'll have to start at both ends of the spectrum and try and find a place in the middle (after years of research and training). You need to start with "surface" aspects like what EQ is used for, what reverb is used for, what compression does and how to use it to mix music. You need to learn about loudness - how to make things loud without making them sound distorted etc.
Then, on the opposite end you'll have to learn the fundamental basics of mixing like how there is a frequency spectrum your ear is sensitive to, from a few hz up to close to 20 000 hz, and that all instruments have a place in this spectrum, in a song. You'll have to learn about how sound moves in a room (different walls/shapes/materials reflect different sounds), about preserving audio quality throughout a mix (record at 48khz, 24 bit, don't go below that unless you have no choice).
And of course you'll have to learn all the technical terms of audio engineering, sound design and recording (convolution, resonance, "boomy", "tinny", "shine", "sizzle"...) plus how to use every single virtual instrument you ever try.
This is a short list but it should give you a HUGE number of leads. Research every term I used here and everything related to all of them. This will give you at least a starting point. The rest is up to you.