Guild Wars 2

I have 26 Tyria Mastery points but can’t seem to use them. Am I supposed to grind experience in Tyria doing the same PVE content over and over again before I can actually use these mastery points? I can’t find a simple explanation anywhere for this they all imply you just need the mastery points.

Yes. You first need to do things that give you experience so that you train a mastery line to the end. Then you spend the mastery point(s) required by that line to unlock the reward at the end.