when i tell you something , and you want to tell me that you understood it , you can say :
# " ana fahim or only fahim " " فاهم - انا فاهم " in English understanding . ( informal )
Also you can say
# " ana afham ma takol" aw " maza kolt " in English " I am understanding what do you say or I am understanding what did you say " . ( formal - standard Arabic )
- Don't say " an afhm or afham " and stopping here because it may seem that somebody asked you in general about your understanding , your mind .
Do you understand ( do you have mind ) ?
- yes , i do ( yes i understand , yes i have mind , afham ! )
* wish i could help !