Questions can be asked directly or indirectly. In an indirect question, a subordinate clause is formed from a direct question:
Direct question: Wie lerne ich schnell Deutsch?
Indirect question: Ich möchte wissen, wie ich schnell Deutsch lerne.

The subordinate clause, which is introduced by an interrogative, is often the object of the main clause. The subordinate clause in this case is also known as the object clause. In sentences composed of a main clause and an object clause, the main clause cannot usually stand alone:
Was möchte Nico wissen?
Er möchte wissen, wie er schnell Deutsch lernt.

As in other subordinate clauses, a comma separates the main clause from the subordinate clause. The conjugated verb is usually at the end of the sentence.

The main clause can be a declarative clause or an interrogative. Look at the examples. Note the punctuation at the end of the sentence: if the main clause is declarative, it has a full stop at the end. If it is an interrogative, there is a question mark at the end.

Declarative clause + indirect interrogative clause:
Bitte sag mir, wo eine gute Sprachschule ist.

Interrogative + indirect interrogative clause:
Weißt du, was dieses Wort bedeutet?

Indirect interrogative clauses are often used to formulate questions especially politely:
Ich möchte gerne wissen, wann der Kurs beginnt.
Können Sie mir sagen, welcher Bus zur Sprachschule fährt?