Not every credit check affects your score. Soft inquiries, like checking your own credit report or a company pre-qualifying you for an offer, have no impact at all and are invisible to lenders.
Hard inquiries happen when you actively apply for new credit, a loan, a credit card, a mortgage, and they can cause a small, temporary dip, typically under five points. The effect fades within a few months and disappears from scoring calculations after about a year.
Many scoring models group similar inquiries made within a short window, such as shopping for a mortgage or auto loan, as a single inquiry to avoid penalizing comparison shopping. This is educational information only.