Your regular rate is not always your posted hourly wage. It includes shift differentials, non-discretionary bonuses and service charges paid to you. It leaves out tips (beyond any tip credit), true gifts and expense reimbursements.
If you work two jobs at two rates in one week, the regular rate is the weighted average. Say you cook 30 hours at $15 and wash dishes 15 hours at $12. That is $630 for 45 hours, a regular rate of $14.00. Your 5 overtime hours are owed an extra half of that, $7.00 each, for $35 more.
For tipped workers under federal rules, the regular rate is the full minimum wage, not the cash wage. That is why overtime at $2.13 comes to $5.755, not $3.195.
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