My book was lost for weeks, but finally it appeared on my table

كان كتابي ضائعاً لأسابيع عديدة، لكن وجدته اخيراً على طاويلتي

بس is originally Persian word means stop but in Arabic we used to mean but. It's better to use لكن which is the Arabic word for but.  

I reviewed the lesson before the exam

راجعت الدرس قبل الامتحان
   
The night fell while we were at the park looking at the view

جنّ الليل بينما كنّا في الحديقة

I couldn't translate the other part of the sentence, because I couldn't reconstruct the sentence in more natural way. 

I lent a big amount of money to a friend

سلّفت مبلغ كبيرة من المال لصديق لي

Arabic Sentences

أحسنت  :)))

جنّ الليل ونحن في الحديقة تفرّجا للمنظر The night fell while we were at the park looking at the view سلّفت مبلغ كبير من النقد لصديق لي I lent a big amount of money to a friend