I'd almost recommend that you do what I did, and take the online Advanced Excel courses at Santa Monica College for like $150.00 each. I'd *almost* recommend it, but I won't, has an ‘F' rating on Ratemyprofessors.com!! Having said that, I did learn quite a few new things – not everything, but enough to get me started on the road to the most advanced aspects of Excel.
Hands-on is the only way to learn it. Passively watching Youtube videos about it is not usually wise unless you just can't figure out how the hell to do something and need clarification. Just go into Excel and create some stuff. Build an amortization table…that is useful for so many things in life. Car/mortgage payments, whatever. Or if you're doing bond problems in FAR, Excel is a great help.
Seriously, I would just get a user manual for Excel and learn all of the important formulas. VLOOKUP, SUMIF, AVERAGEIF, INDEX-MATCH, etc. Don't bother with the math-related ones or the hard-core statistical ones unless you're doing auditing or something else where you need to know them, then learn them. Also using GoalSeek and the other optimization-type commands is useful. One thing I need to learn how to do is write macros. Those who know how to do that are much the better for it. You need to know Visual Basic. Being able to build templates and forms in Excel is also a very useful skill (templates that other people can complete or use to upload data to other software programs as .csv or .txt files.)
It's interesting for me – I learned one aspect of Excel for my first BS degree in Chemistry (statistical analysis) and another aspect of it for Accounting (VLOOKUP and HLOOKUP, pivot table, etc.)
I love Excel. I use other softwares for different things in my job but that's always my favorite. Very powerful and at the same time, not hard to use. Part of learning it is making mistakes in it and playing around with formulas that maybe don't work for you right away.