Well it's depending of youor understanding for the sentence.. *you only put it if you mean a specific thing / person.. etc Eg. If you mean that school (your school ) you are talking on specific thing so you say when you want to say ( I went to the school ) ذَهبتُ إلى المدرسة *when you add for the word something make it known/specific never add ال As adding pronoun Eg. If you mean to say -your school - and you have already added the pronoun -my- to school then (my school ) become مدرستي So you never add ال with word has pronoun Also as add any word which is not Na'et / adjective as Eg. If you mean to say - house of elders - you say دار المسنين Focus on that you can add more than one word and the only word you add ال for is the last word as (The street of flowers of life ) becomes ( شارع ورد ال-حياة ) As you saw street - شارع was followed by flowerورد , also flower ورد was followed by life الحياة but the last word wasn't followed by any thing so we put it with ال In general.. you add ال for known nouns except those which follow by another noun which make them more specific..

في اللغة الإنجليزية تسمى هذه الأدوات articles وهي مقسمة إلى قسمين : the"(1 " وهي توازي "ال" التي تبدأ بها الأسماء المعرفة في اللغة العربية. الكتاب the book المنزل the house السيارة the car a" (2 " وهي توازي الأسماء الغير معرفة في اللغة العربية. كتاب a book منزل a house سيارة a car

It's like the english article "the". When there's no article it's equivalent to the english article "a/an".