How do you say i not understand in Arabic?

There are several ways to say "I don't understand" in Arabic, depending on the level of formality and the dialect. Here are a few options:

* Formal: لا أفهم (lā afham) - This is the most common and grammatically correct way to say it in Modern Standard Arabic (MSA).

* Informal (Egypt): أنا مش فاهم (Ana mish fahem) - This is a common way to say it in Egyptian Arabic.

* Informal (Levantine): ما فهمت (ma fihimt) or أنا ما فهمت (ana ma fihimt) - These are common ways to say it in Levantine Arabic (Syria, Lebanon, Jordan, Palestine). The second one is slightly more emphatic.

* Informal (Gulf): ما فهمت (ma fihimt) - Similar to Levantine Arabic.

The best option depends on the context and who you're talking to. If you're unsure, لا أفهم (lā afham) is a safe and universally understood choice.