Rules - Relative Clause and Relative Pronoun

Relative clauses are subordinate clauses which describe a person or an object in a more detailed way. The relative clause always follows the main clause, directly (or as close as possible) after the word it refers to.
Main clause	Main clause
In dem alten Haus wohnt ein Mann.	Er hat einen schwarzen Sportwagen.
Main clause	Relative clause
In dem alten Haus wohnt ein Mann,	der einen schwarzen Sportwagen hat.

Relative clauses are introduced with a relative pronoun.

Gender and number (masculine, feminine, neutral, Plural) of the word the relative
clause refers to in the main clause and the function of the relative pronoun in the
relative clause decide on the relative pronoun.

		The word the relative clause refers to decides on:
		Singular masculine	Singular neuter	Singular feminine	Plural
The function of the relative pronoun decides on:	Nominative	der	das	die	die
	Accusative	den	das	die	die
	Dative	dem	dem	der	denen
	Genitive	dessen	dessen	deren	deren

If there is a verb with a preposition in the relative clause, the preposition
is placed before the relative pronoun.

Main clause	Relative clause
In Ulm fand der erste Deutschkurs statt,	an dem ich teilgenommen habe.