The short words that carry much of the load in Arabic.
One Arabic preposition often covers several English ones, depending on context.
مِنْ vs عَنْ — مِنْ marks a literal source or starting point ("from the earth"); عَنْ is looser: about something, or away from it. إِلَىٰ vs حَتَّىٰ — إِلَىٰ marks a destination; حَتَّىٰ marks "until" a point in time or degree, and can introduce a "so that" clause.
A preposition puts the following noun in the genitive case, which is why you so often see a kasra on it.
بِ, لِ and كَ are never written as separate words — they attach directly to the front of the noun.