Dramatic Irony is irony based on you knowing something the characters don't know. If you've ever seen a horror movie, or a Nicholas Sparks romantic drama, you know what I'm talking about. Examples would be knowing that the blonde character is about to open the door to the room that Jason is waiting in, or the husband coming home to see his wife when we clearly know she remarried while he was off.
So, asides are the main way a storyteller is able to communicate dramatic irony for tension, weather it be dramatic or comedic. Lets go back to the Friday the 13th analogy. The main story involves the teenagers at camp Crystal Lake. So while we'll have a scene fleshing out their characters in the dining room, we'll cut away to an "aside", or scene/plotline that's not directly related to the main plot, of Jason crawling in the window to the bathroom. We then cut back to the main shot, where the blonde character says she needs to relieve herself. Everybody laughs, and as she walks away, we see Jason inching towards the door with machete in hand. The side-plot, or "asides" of Jason getting in the room, builds the dramatic irony of us knowing the blonde is going to die, but the characters don't know that yet as the asides were out of their realm of perspective.
