You own a successful company. Someone is asking you about how you started the company and paid to build it up. They ask if you got investment money from someone. You didn't, so you answer:
I financed the entire company out of my own pocket.
To "finance" something means to get or provide the money to pay for it. This word is only used for expensive things, like starting a company, building a factory, etc.
The word "finance" is interesting because it is used both with the person who's giving the money for something and for the person who's getting the money:
Our expansion is being financed by a private investment company.
I financed my education through a mixture of scholarships and student loans.
"Entire" means "whole" but is more formal.
To pay for something "out of your own pocket" means to pay for it with your own money. This is a common expression that's easy to remember if you imagine carrying all your money around in your pockets, and then pulling the money out of your pocket to pay for something.
You can only talk about someone paying out of their own pocket:
She paid for the trip out of her own pocket.
It doesn't make sense to talk about one person paying out of another person's pocket.
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