It really depends on what you will use it for. Using it for plain text doesn’t require much, some advanced layouts require a bit more digging, if you’re including fancy graphics, equations, bibliography, footnotes, etc, you’re going to look at managing the relevant libraries to gandle that (they are very well made and very convenient). All in all, it can be as complex as you want, but it can also be quite easy to use.
Also LaTeX is way simpler than plain TeX.