A verb placement is based on subject reference
Position 1
The verb HAVE is usually is in [POSITION 1] in the sentence:
"Ich habe einen Hund"
"I have a dog"
Interrogation. Subject in position 2
With interrogative sentences
the verb HAVE takes [POSITION 1]
which is why it moves the subject to [POSITION 2]
"Hast du einen Hund?"
"Do you have a dog?"
Subject inversion. Position 3
To emphasize a complement or an object
HAVE can be placed in [POSITION 1]
which makes the subject move to [POSITION 3]:
"Einen Hund habe ich"
"I have a dog"