Learn Arabic (Modern Standard): العديد من السكان يستخدمون الحافلة يوميا.

Both mean "many" or "a lot of," but العديد من often sounds slightly more formal and translates closer to "numerous." At this level, you can use them interchangeably in most contexts.

What is the singular form of السكان (the residents)?

The singular is ساكن (sakin). The plural سكان is a broken plural pattern often used for people performing an action, having a profession, or occupying a state (similar to عامل / عمال for workers). It comes from the root for dwelling or living.

Could we start this sentence with the verb instead?

Yes, but the verb would have to change! If you start with a verb (Verb-Subject order), Arabic rules require the verb to stay singular. It would be يستخدم العديد من السكان الحافلة يوميا. Because our sentence puts the subject first, the verb must match it in number and become plural (يستخدمون).

How does the Form X pattern in يستخدمون relate to its root?

Form X verbs (which start with است / ista- in the past tense) often mean "to seek" or "to utilize." Here, يستخدمون comes from the root خ د م (kh-d-m), which is all about serving (like خدمة, service). So, it literally means "they utilize" or "seek the service of" the bus.

Why does (daily) have the double marks (tanwin fatha) at the end?