For this guide there are a few routes laid out in front of you. Each route has its own explanation in its own page. It might be worth checking each route as knowledge shouldn't be limited to just one route.
In general, you want to go through the Adventurer route first. (Learn the kana.) Once done, you wanna go to either the Sage or the Runner route. The Sage page has the section on grammar so you would want to check out that page regardless.
The Talker route is for people who want to take the language more verbally.