What does it mean to fear God?

Job 13:11
Shall not his excellency make you afraid? and his dread fall upon you?

Psalm 33:8
Let all the earth fear the LORD: let all the inhabitants of the world stand in awe of him.

Psalm 128:1
Blessed is every one that feareth the LORD; that walketh in his ways.

Proverbs 9:10
The fear of the LORD is the beginning of wisdom: and the knowledge of the holy is understanding.
Fearing God is not the same as being afraid of God. Being afraid of someone drives you away from that person. Fearing God means being awed by his power and goodness. This draws you closer to him and to the blessings he gives. Fear of God like the respect you have for a beloved teacher, coach, parent or mentor who motivates you to do your best and avoid doing anything that would offend them or provoke their displeasure. You fear God because of his awesome power; you love God for the way he blesses you with it. And this brings great joy.

2 Corinthians 7:1
Having therefore these promises, dearly beloved, let us cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God.
A healthy fear of God motivates you to strive for holiness.