Divide the diagram into connected regions by connecting dots. Each regions must contain every letter exactly once. Next to the puzzle you see which letters are used. Some puzzles contain question marks. A question mark can represent any letter.
First of, we can start by drawing lines separating the neighbouring Bs and Cs. Also, notice that the A in the bottom right has only one C that is close enough to be in the same region, and there is only one region that can contain both of them without having another A in it.
Now, the top left A must be connected to the C and B to the right. We don't know which D it needs yet though. However, if it would have the D to the bottom, then the top right D would be forced to connect to two Cs. So, we must use the D to the right in stead. The remaining area can now only be split in one way.