The detailed link has been provided, but simply, hit your trait key.
A window will pop up with the three trait lines just like the old days, the difference is now you have to select one as your "specialty". That's what that means.
There are overviews of the difference, either pick which you want, or pick the same one you used to use back when you had to go to bards to trait.
Then start clicking in the same color for the traits/abilities/skills you want. You may also pick from the other colors/specialties, but you'll see each costs twice as much.
Click apply, done.
Alternatively cancel and redo. You may also right click to get points back before you apply.
If you accept, then re-spec, don't be shocked it'll cost more than it used to with bards (almost a gold at level 74).
You can now have multiple specs, and freely switch between them anywhere out of combat.
Note, when putting points into things, don't feel overwhelmed, as you really have very limited choices, and things have prerequisites you have to spend on to gain, so your hands are tied, which makes it easy since you don't have to decide anything, just click a bunch of times until you get what you want.
PS: The 300% damage value being threat is really irrelevant, you can't affect that number, it is a behind the scenes scheme. If you want to know more about threat changes, there's a link within the guide to change above. Basically as a guard in a tank spec, you innately have threat, all of your skills provide threat, and you rely on force taunts to grab MOBs.
Link to our community LOTRO store google spreadsheet pricelist and conversion rates, please contribute too!: https://goo.gl/wxPqCm