User (Customer) Journey vs User Flow

First - these are tools, next to personas creating.

User Journey is a scenario - how (showing possible ways) a user interacts with the product, in 4-12 steps.
User Flow is a process - how (showing designed templates) user uses the product to achieve his goals.

Both are for UX designers to help to understand (clients needs, goals) better and design product better. Both are about what user want to achieve, how the user wants to use the product and what for (behaviors).

User Journey is about a complete process (finding a product, compare it with similar, buy, use). User Flow is about using the product (e-commerce website or app OR TV set you can buy there - for example).