Hi
Apple Pay is available within selected countries:
http://www.apple.com/ios/feature-availability/#apple-pay
If you are within one of those regions, check that your iPhone region is set accordingly, in order to see the option to add cards to Apple Pay:
On your iPhone, go to: Settings > General > Language & Region > Region.
Also follow all of the required steps here:
Set up Apple Pay on your iPhone, iPad, Apple Watch, or Mac - Apple Support
Note that it is also only possible to add supported payment cards from participating banks or stores within those countries.
More information:
Apple Pay participating banks in Canada and the United States - Apple Support