Structures with the word КОТОРЫЙ

Let's talk about structures with the word "который" [katoryy]. It is very important part of the language because this word has a wide range of meanings and it is rather difficult to translate it into your native language unambiguously. The word "который" can have the same meanings as the words "какой" (which), "что" (that), "кто" (who). In this case you should always understand the context. The issue of agreement is also difficult one.

Let's begin with the fact that the word "который" is changed in gender and numbers and declined in cases. Changing of the word "который" is typical for the words with the ending -ый.

который - которая - которое - которые [katoryy - katoraya - katoroye - katorye]
Nom. который - которая - которое - которые
Gen. которого - которой - которого - которых
Dat. которому - которой - которому - которым
Acc. которого - которую - которое - которых
Inst. которым - которой - которым - которыми
Prep. котором - которой - которым - которых

It is more important to mention that the word "который" agrees in gender with the word written before it and in case with the word (or phrase) followed by it.
Это начальник, которого мы ценим - This is the boss who we respect.
Это наша дочь, которую мы обожаем - This is our daughter who we adore.

If you deal with a compound sentence and it is difficult for you to define a correct form of a word, then divide a sentence into clauses. The punctuation will help you - we use commas in the structures with the word "который", we write them as before the structure as after it.

Машина, которую я купил - The car, which I've bought.
Машина, которую я купил, всем понравилась - Everybody likes the car, which I've bought.

After that, look at the word before the structure and after it. Define number, gender and case.

Я прочитал книгу, которую ты дал мне - I read the book, which you had given me.
Это мой друг, с которым я учился в школе - This is my friend with whom I used to study at school.