Interval names (”perfect fourth,” “augmented sixth”) can be confusing at first. The key to understanding is 1) think in letter names, 2) put C in the middle. I’ll walk you through a simple visual explanation.
When played as a “sus2” chord or a “sus 4” chord, it can behave in one of two ways: it can serve its stated purpose by suspending resolution to a more stable chord, or it can connote the open sound of an acoustic guitar.
The augmented triad has the interesting quality of inverting onto itself—that is, if you take the triad in root position, and put the bottom note on the top, you get another augmented triad in root position.