Well it has to do with preposition construction as said before. Depending on the case, the meaning of a preposition changes with it. However, they do not always change to a different meaning for every case - only a few of them. For example:
"ha"ha janaan = for the dog
ha janoon = from the dog
"mra"mra okraan = into the tent
mra okroon = out of the tent
"she"she hrazef = on the horse
she hrazefaan = onto the horse
she hrazefoon = off of the horse
irgeirge athlajari = after the fight
irge athlajaraan = to the back of the fight
irge athlajaroon = from the back of the fight
Those are just a few but I think you get the point. Ma is an interesting case, because it functions as both a preposition and a conjunction. This is also true of haji. Really the best thing you can do is memorize the prepositions table; they can be difficult to understand at times but I'm sure you'll get the hang of it!
You seem to be quite prolific at beginners Dothraki and I think it's time you did some research into the more difficult grammar rules of the language. I went onto the Wiki homepage for Dothraki, and took notes (by hand) of every article on the website about dothraki that I didn't already have. It would benefit you greatly if you are truly dedicated to Dothraki. If you want to, I would be happy to have conversations with you over Skype like I do with other members of the forums.
Here's the link to the prepositions table:
https://wiki.dothraki.org/PrepositionsHere's a link to the Dothraki grammar:
https://wiki.dothraki.org/Learning_Dothraki#Grammar