When a third party looks at your credit score, this is called an “inquiry”. A “soft inquiry” does not affect your credit score, but a “hard pull” does. Limiting your hard pulls will qualify you for the best interest rate available when you apply for a loan.
Here are some soft inquiry examples:
Your credit score will not be affected if you check your own credit report. You should confirm the accuracy of what is being reported about you, and you can do so for free once per year from each of the three credit bureaus at: https://www.annualcreditreport.com (there is a nominal charge if you want to see your score).
When you apply for a loan or a new credit card, however, the lender or mortgage broker will conduct a hard pull on your credit report. A hard pull stays on your record and it lowers your credit score by about 5 points for six months. For these reasons, it is important to guard your credit report from too many hard pulls. So if you get a store credit card just to save 10% on a single purchase, know that you have hurt your credit score – and it is probably not worth the savings.