Basically, a barre chord is when you use one or more fingers to barre the several strings at once. For example, the F Major chord shape is a barre chord, because you use your first finger to barre all the string, (although you don't actually play three of the six strings fretted with your first finger)

Sorry to treat you like a fool, but just in case you don't know what an F Major Chord looks like

-1---
-1---
-2---
-3---
-3---
-1---

just like that....
Now, a Power Chord is even easier....All it is is the Root of a scale, and the 5th, with and optional octave root (same pitch, twelve notes higher). They're usually played with the root either on the 6th or 5th string....

G---------9-------7--
D--3--6---9---2---7--
A--3--6---7---2---5--
E--1--4-------0------

---F--G#--E---E---D--

You'll notice the shape stays the same, so they really are very, very simple....

Hope I've helped, not confussed you.