That is a bad homework, and it suggests the teacher doesn't understand how Wikipedia works either. Wikipedia is a collaborative effort, and some parts are out of your control. Including possible nominations for deletion.
Anyway: Pick a topic you know something about, that makes it much easier. The English Wikipedia has
article requests, the Arabic equivalent is
ويكيبيديا:مقالات مقترحة. These lists usually contain important topics that don't have articles yet. Alternatively you can pick any article in the English Wikipedia and check if there is an Arabic article for the topic (check the Links at the lower left, that's how I found the Arabic version of the article requests). A translation of an existing article in a different language is easier than writing an article from scratch.
Both the English Wikipedia and the Arabic Wikipedia have help pages how to write an article, the English one has much more about it (as it is much larger).