How do I install Apple Pay

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)

Make purchases using Apple Pay

Make purchases using Apple Pay - Apple Support

Make contactless payments using Apple Pay on iPhone

Use Apple Pay for contactless payments on iPhone – Apple Support (UK)

Use Apple Pay in apps, App Clips, and Safari on iPhone

Use Apple Pay in apps, App Clips, and Safari on iPhone – Apple Support (UK)

Set up and use Apple Cash on iPhone (U.S. only)

Set up and use Apple Cash on iPhone (U.S. only) – Apple Support (UK)

Manage Apple Pay cards and activity on iPhone

Manage Apple Pay cards and activity on iPhone – Apple Support (UK)

Read and follow the article linked above.