Files don't open in the app I want

In Finder, double–clicking a file opens it in the app associated with its type. You can Ctrl-click the file instead and pick a different app from the Open With submenu, or drag it onto an app’s Dock icon.

To make all files of a type open in a particular app, select one and press Cmd+I to open a Get Info window, pick an app under ‘Open with’, then click Change All for your pick to take effect.