Wrong!
Every hard inquiry on your credit file briefly lowers your score. "Hard inquiry" occur when you apply for a credit card, car loan, mortgage, etc. They can also happen when you apply to rent an apartment or open an insurance policy.
Soft inquiries have no impact on your score. "Soft inquiries" include promotional inquiries (those credit card and insurance offers you receive in the mail), ongoing inquiries by your credit card issuer (periodically checking up on you), and all the times that you examine your own credit report.
Temporarily, and not much unless you have 10-15 pulls in a short period of time.
Checking your own credit does not ding your score.
That is a commonly held misconception. If you are shopping for a mortgage or an auto loan, a number of credit checks from various inststutions over a reasonable time period are expected. You are, after all, only seeking one mortgage or car loan. On the other hand, if you are shopping equity loans, personal lines of credit and new credit cards all at the same time, that becomes a red flag to the lenders.
Only partly true - when you check your own credit, there is absolutely no effect on your score.
Even when another company does a "soft" inquiry on you, for account reviews or promotional inquiries, there is still no effect. The only inquiries that make any difference are "hard" inquiries, which happens when you actively apply for credit. Nowadays, when you open a bank account, they may also check your credit in that way as well, which also counts.