When to use paid and paid?

Answer 1

Both paid and payed are the past tense of pay.

Payed is not commonly used payed is more or less obsolete.

present - I always pay my bills on time..

past - I paid for my ticket then had a drink at the cafe.

Answer 2

"Paid" is the past participle of the verb "pay" and is used with auxiliary verbs such as "have" (e.g. "have paid"). "Paid" is used as an adjective or a verb form, while "payed" is an old and rarely used variant.