A limited liability company is a business formed under state law. You
file articles of organization with a state, the state registers the
company, and from then on contracts, debts and bank accounts can sit
in its name rather than yours. For a freelancer who works alone, that
is a single-member LLC, and in most day to day respects the work does
not change at all: you still find the clients, do the job and send
the invoice.
What changes is the paperwork around the work and where the risk sits.
The company becomes the party to your contracts. You keep its money in
its own account. You file a short report with the state on a regular
schedule. In exchange, a debt or claim against the business generally
stops at what the business owns, rather than reaching your savings or
your home.
What does not change, by default, is your federal tax. The IRS
disregards a single-member LLC unless you elect otherwise, so the
profit lands on your personal return in the same place it did before.
That surprises people who formed the company expecting a tax saving.
An LLC separates the business from you. It does not, on its own, change how much tax the business pays.