Janie Kliever at designschool.canva.com:
Have you ever looked at a word or phrase you’re typesetting and something just looked off about it?
It might just be a kerning problem. Kerning refers to the amount of space between two letters (or other characters: numbers, punctuation, etc.) and the process of adjusting that space to avoid awkward-looking gaps between your letters and improve legibility.
It’s important to note here that kerning is a visual exercise; it’s about the perceived amount of space between letters rather than the actual distance between them. Kerning involves adjusting your typography to look right rather than creating mathematically equal spacing.
Kerning may seem like an unnecessary or unimportant detail, but adding it as a quick extra step at the end of your design workflow can make a big difference in helping typography-focused projects look polished.
Software has gotten much better at kerning and word spacing but a bit of manual kerning is still sometimes necessary to make it look "right." It's also important to remember that not all software is the same. And even if you use the right layout software with the right settings, you can still be let down by a poorly spaced font.