How do I apply my Apple cash to my bill

See the following Apple articles:

Set up Apple Pay

Set up Apple Pay - Apple Support

Countries and regions that support Apple Pay

Countries and regions that support Apple Pay - Apple Support (EG)

Set up Apple Pay in Wallet on iPhone

Set up Apple Pay in Wallet on iPhone – Apple Support (UK)

I presume you mean to Apple Card. When you select your card payment amount your Apple Cash will be displayed as part of the payment.

Read again -> Related Article

Add money to Apple Cash

Have iPhone need to pay merchant with Apple Card ? In iMessage

how do I do that ? Through Apple Pay wallet ? I dont want a apple credit card . How do I get this apple Visa card ??

How do I do this ??

I wouldn’t pay any merchant using Apple Cash. Apple Cash is for private party transactions. If there is an issue with the product, you have no recourse.