Website for learning Excel

I want to learn how to better use and understand Excel. I was recently helped out by shg and FDibbins in my previous post.

However, I am having troubling understanding how each command function works in a formula (example below). I have been googling each part of the formula and I now understand (mostly...) how it works. Just don't ask me to try to utilize it in different situations lol. Is there a website that you all recommend for learning? I used GClearningservices but it mostly shows you how to do mathmatical functions (something that I can do already). I was also wondering if there is a website where I can just plug in formulas and it will spit out this part means this and this means this etc.....

=COUNTIF(B3:B5, LEFT(B4, LEN(B4) - 1) & IF(RIGHT(B4) = "A", "B", IF(RIGHT(B4)="B","A"))) = 1

Thank you for your time.

Looks interesting, thank you!