Click on ADD A GADGET.
Scroll down the list and click the plus for Label.
Decide how you want your labels to look.
Then save your gadget. You can move where your gadgets are placed by dragging the rectangle where you want it to be and then save your arrangement.
To add a label you write your post and add the label that you want your viewers to see. like this...
Your labels will then look something like this...