Looking at the lower right of your page, you will see a heading labeled "Vote".
Looking at the lower left of your page, you will see a heading labeled "Our World Rankings".
Below each of these sections you'll find the following links:
Upon clicking one of those links, a voting site will open. Follow the directions on the site, sometimes just voting isn't enough.
Now comes the fun part of what to spend it on:
+1 Energy [1 AP] - Gives you Energy
+1 Mythril Ore [1 AP] - That can help to make Mythril
+1 Faith Point [1 AP] - That can be used for Faith
+0.5 Strength [10 AP] - Gives you Strength
+0.5 Agility [10 aps] - Gives you Agility