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How Dose A Chaos Space Marine Become A Sorcerer, Dose He Gain His Abilities Form The Chaos Gods?

they are psykers, the same as the Imperium. They can have their powers enhanced by the Chaos Gods though.

Look at Typhus for an example, he was a psyker (albeit a secret one) who had his powers enchanced by Nurgle.

Psykers draw power from the warp. Chaos sorcerors enhance this by making pacts with daemons for additional powers, using "sorcery" and occult practices.

They channel the warp through the planet they're on making their power variable. It's the reason they lose battles they should have won - plot armour is a myth.
Or they generate it with a one armed bandit, odds are about the same.

Daemonic pacts, arcane items, awakened latent psychic powers... basically any narrative you can force into the role!

The general principal is the same as Imperial psykers, but more specialized depending on which god they may pay tribute to or have a pact with.

The warp is the fuel for most sorcerers. 'Winds of magic' is a good way of thinking about it, introduced in Warhammer Fantasy.
Magic is all around people, because the warp is an alternate dimension to the current world. All you need to do is cut a hole in the wall between words, and use the power there, to affect the here. Of course only sorcerers and other psykers can do this. And even then, something else could always claw itself through that hole.