The suffixes -Dİk and -(y)EcEk are used when relativizing:

The direct object
The indirect object or the adverb
The possessor of a genitive-possesive constituent which is not the subject
The possessed of a genitive-possesive constituent which is not the subject

The difference between -Dİk and -(y)EcEk is that -(y)EcEk refers to future events, whereas -Dİk refers to non-future events, for example events in the past or in the present. Just as with -(y)En, adverbs are used to give detailed information about the time an event occurs.

Clauses with -Dİk and -(y)EcEk are always genitive-possessive constructions. Below you can see two sentences where the direct object is relativized.

Full sentence	Relativized version
(Ben) makale okudum. I read an article.	(Benim) okuduğum makale The article that I read
Kamil makale okuyor. Kamil is reading an article.	Kamil'in okuduğu makale The article that Kamil is reading

Note how the subjects of the sentences have become the possessor and the objects of those sentences have become the possessed part in the genitive-possesive constituent. If the subject of the relativized sentence is a pronoun, it can be omitted both in the original sentence, and in its relativized form.

Below are examples of both -Dİk and -(y)EcEk when relativizing a direct object.

Full sentence	Relativized version
Makaleyi okuyorum. I'm reading the article.	(Benim) okuduğum makale The article that I am reading/have read
Ödevimi yapacaksın. You will do my homework.	(Senin) yapacağın ödevim My homework which you will do

Below are examples of both -Dİk and -(y)EcEk when relativizing an indirect object.

Full sentence	Relativized version
(Biz) mektubu öğretmene vereceğiz. We will give the teacher the letter.	(Bizim) mektubu vereceğimiz öğretmen The teacher to whom we will give the letter
Çocuklar ayılardan korkarlar. Children are afraid of bears.	Çocukların korktuğu ayılar The bears that children are afraid of

Note how the case suffixes on ayılar and öğretmen disappear when in relativized form.

Breakdown of Mektubu vereceğimiz öğretmen