Learn Arabic (Modern Standard): لا تركضي بالمقص في البيت. - Do not run with the scissors in the house.

This is the negative command form taught in this lesson. When we use لا to tell someone not to do something, the following verb goes into the jussive mood. For the feminine "you" form, the normal present tense verb is تركضين. The jussive mood drops that final ن, leaving us with لا تركضي.

Who is being addressed in this sentence?

A single female. We know this because of the ي suffix at the end of the verb تركضي. If you were giving this same negative command to a male, you would say لا تركض and put a sukoon (a marker indicating no vowel sound) on the final letter instead of adding a suffix.

Why does the Arabic say بالمقص using بـ instead of the word مع for "with"?

In Arabic, the prefix بـ is used when "with" refers to a tool or instrument you are using. The word مع means "with" in the sense of accompanying someone, like "I went with my sister." Since the scissors are the instrument here, we attach بـ to the word for scissors, المقص.

How do you pronounce the beginning of بالمقص?

It is pronounced "bil-miqass". When the prefix بـ attaches to a word starting with the definite article ال, the first letter of the article is silent. You jump directly from the "bi" sound of the prefix to the "L" sound.