I get that everybody has different learning styles, and I personally find videos excruciatingly tedious and useless, so I admit that I’m heavily biased against them. I’m sure there are good ones out there, but I can’t give any recommendations because they are definitively not my cup of tea.
Some key terminology notes here:
People do it as shorthand, but “Ionic” isn’t a monolithically versioned thing, so it can cause confusion to speak of “Ionic 4”. More detail here.
“AngularJS” describes a now-pretty-obsolete-and-should-probably-be-ignored-by-somebody-in-your-position version of the framework that is now just glossed “Angular”. Version 1 of the Ionic Framework used AngularJS. Nothing thereafter did, so I would strongly suggest aggressively avoiding any resources referencing “AngularJS”.
If you’re going to use Ionic with Angular, it is crucial to be grounded in Angular itself. I think the single best resource for this is the Tour of Heroes. If you get all they way through that, you should become familiar with the key building blocks you’ll be working with and what idiomatic Angular code looks like.
As for Ionic-specific stuff, the quasi-official Ionic showcase is the ionic-conference app. I would suggest looking to it to crib idioms surrounding any Ionic component you’re particularly interested in.
This may seem like I’m blowing off the code snippet you posted, and that may be frustrating. It is, however, a fair assessment of the situation, and the reason I’m ignoring it is that the has-header attribute on ion-tab-bar hasn’t existed since v1, so I fear that you have a bunch of frankencode that would probably be better off left in the dust with a fresh start.