Here's my take on it.
Right of the bat, Danie starts off with a clever joke. The angel tells Satan to freeze. In Hell. Obviously this is not possible given the ambient temperature there (about 10,000 degrees Kelvin). Either the angel is indeed dumb (as the title suggests) or it is a jest on the part of the angel.
Satan appears to be threatened by a mere angel. Why? Given the spelling in his thoughts, I can only conclude that he is drunk and his dark powers are low. Perhaps his vision is blurred and he has mistaken the Angel for the Almighty. We see in the second panel that he refers to the angel as "Sir."
The angel recognizes this ("Are you kidding?") but asks for directions anyway.
In the last panel we have our punchline. Satan gives directions by masturbating furiously, as indicated by his grunts of pleasure. The jism splatters off-panel in the direction of the Pearly Gates. Indeed, given the power of Satan's orgasm I think we can infer that those far-away gates are splattered by Satan's love juices.
The angel sees the trajectory of the flying wigglers and bids Satan farewell. No doubt the angel will be forced by St. Peter to clean off the gates later with his tounge.
Danie has in three panels explained the old W.C. Fields saying, "Never ask Satan for directions to Heaven when he's drunk, or you'll have to lick his sperm off the Pearly Gates."
Well done!
---
...Trot and Cap'n Bill were free from anxiety and care. Button-Bright never worried about anything. The Scarecrow, not being able to sleep, looked out of the window and tried to count the stars.