How do delivery drivers for pizza and Walmart groceries, etc., get paid?

How do you think they are paid?  Their EMPLOYER pays them.

Some are employees of companies that give them money to do the job.  Others may be independent contractors who bill their clients for the money to do the job. Some people deliver food to the homeless, shut-ins or needy as volunteers, meaning they don't get paid money, but get other rewards for their good deeds.

Tip whatever amount you are willing to give.  There is no formula.