You are both the client and the designer for this.
You give them a set of questions to answer and meet with them (via phone or in person).
Most designers call this the "Onboarding" of the client. Meaning familiarizing a new customer or client with one's products or services.
At this point you will have to convince them why you are the solution to their problems. Everyone who is in business has a "problem" to solve. It could be that they need young people to start buying their product or they need to have art that appeals to people who eat clean.
The people that come to you for help will not typically know how to code, create a user interface (ux), draw a logo, arrange a catalog, design stickers/labels/packaging, etc. They need someone like you to help them.
Don't take this role too lightly. If you give them a crappy product (logo, book cover, etc) they will lose money and you will lose their business.
Some people choose to start by working for a company so that the work load is distributed over a larger group of people.
Some choose to go freelance and do all of the work themselves.
Just make sure that you start with doing the reasearch.
Here are the questions you need to have answered in order to help this company reach it's target audience:
What do you offer in plain language (their brand)?
What is the coolest thing about your brand?
What are your core values?
Who is your target consumer?
Describe the competetion? How are you different?
What emotions should your brand evoke?
If your brand were a person who would it be?
What words best describe your brand?