Register an LLC or corporation with your state and keep it in good standing.
Business credit attaches to a legal entity, not to you personally. No entity, no file to build.
File through your state's Secretary of State (or business-filing) office and keep the entity active.
Source: Your state Secretary of State + IRS (irs.gov)
State filing fee — a Texas nonprofit corporation is about $25; LLCs vary by state
The EIN is the business's tax ID — the "SSN of the business" that bureaus and banks key to.
This is general business-credit education, not financial, legal, or tax advice. Confirm specifics with a licensed professional and the official sources directly.