In plain English
The separation is the point. The company signs the lease, holds the bank account, owes the suppliers and builds the credit history.
That separation only holds if you maintain it: separate accounts, separate records, and business expenses paid by the business.
Example
You register an LLC with your state, get an EIN, open a business bank account in the LLC's name, and buy inventory from it.
Why it matters
Suppliers, landlords and banks extend credit to entities with a history, not to a personal name with a nickname on the invoice.
COMMON MISTAKEForming the LLC and then continuing to run everything through a personal account.