What does Fortification do?

Solution 1:

Fortification is, as the wiki describes, an alternative Barrier skill that gives an Armor bonus.

Fortification reinforces armor with a non-Newtonian fluid that hardens when struck, providing a brief, huge bonus. Reinforce armor using protective Foucault currents.
Purge the current and send its charge to your gauntlets for increase melee damage.

• Slows power usage by 60%.
• Damage Reduction: 15%
• Melee Damage Bonus: 50%
• Melee Damage Duration: 20 sec

You can see the Power Ranks for Fortification at the Wiki too.

Solution 2:

Fortification and Tech Armor are similar powers - both have a 2-stage activation.

When you first activate the power, you gain the defensive bonuses. This allows you to charge an enemy position. Once you've gotten into melee range, you can press the button again to (in Fortification's case) channel the power of the defensive bonus into a melee bonus.

The drawback of having the defensive bonus is that your power cooldowns will be increased. This is to keep you from just leaving the barrier up continuously.

Tech Armor has similar effects, except that unlike Fortification's melee bonus, Tech Armor detonates a small shockwave around you when you set it off instead.