doblar, verb:

to fold; to bend; to turn

Doblar has several interconnected meanings. First, to fold something.

Doblé las sábanas y las guardé.
I folded the sheets and put them away.

When talking about bending your arms or knees, doblar also applies:

No podía doblar la rodilla por el dolor.
I couldn’t bend my knee for the pain.

A distantly related meaning is to turn from one direction to another:

Cuando llegues* al cruce, dobla a la derecha.
When you reach the junction, turn right.

Notice the phrase, doblar la esquina to turn a corner:

Al doblar la esquina de su casa vio el reloj.
When he turned the corner of his house he saw the clock.