Business credit is the borrowing record of the company itself, held separately from the owner's personal credit.
Why it is separate
A newly formed business has no record, so early borrowing is usually underwritten on the owner personally, or guaranteed by them. Building a company record is what eventually removes that.
The separation only exists if it is maintained. It requires a genuine legal entity — see business entity types — with its own bank account, and business costs kept out of personal accounts and personal costs out of business ones.
What builds it
Accounts held in the business's legal name with its own identifiers.
Supplier accounts on net terms that report payment history, which many suppliers do and many do not. Terms that are not reported build nothing.
Paying early rather than on time. Some business credit scores are calculated on days beyond terms, where paying on the due date is neutral and paying ahead of it scores better.
Time
Credit is built over years, not months, and it is another reason to arrange a line of credit before there is a need for one.