I have no idea hat airdashing means. Hell couldn't beat the MK11 tutorial either because the combo tutorial was fucking stupidly complex.
When you hit forward twice in quick succession the char moves forward much more quickly than if you just hold forward, think of it like the difference between running and dashing in Sekiro. Some games let you dash infinitely by holding down that second forward input (and allow you to control when to stop dashing), others make the dash a pre-set distance.
Some games incorporate more air mobility in them than others, and some games let you air-block grounded attacks and others don't, which completely changes the dynamic of the game. Included in this category are games in which you can not only air block grounded hits but if you input the grounded dash input while airborne you get a pre-set air-dash that changes your trajectory while mid-jump (so like, I jump forward, grounded guy tries to hit me, I dash back, he misses, I punish his missed hit, tons of options open up), which furthermore completely changes how they play.
A typical game with that system mechanic and generally speaking an anime aesthetic is referred to as an airdasher (or an anime fighter but that's too imprecise and may confuse people into thinking it applies to stuff like those naruto arena battlers and so on).
I legit dunno anything about MK but either way, fighters are complex so you're not supposed to master everything in the tutorial in one go, especially not if you're new. You just wanna do a bit of it to get the gist of the game, then play some matches, then if you have something that you don't understand you revisit that tutorial again, over and over and eventually you'll learn everything. Hell, some people just jump into matches right away and learn as they go. You don't need to understand all the most complex stuff there is, a lot of it is there for the experienced players who already have the basics drilled into their head through thousands of hours of practice and wanna learn how this GG is different than the last 4 of them.