Mobile App Apis

i want to build a new customized mobile App for my platform ,,, i want to know how can i link products , categories, login , shipping and payment methods through API ,,, how can i reuse these API form my customized APP

any help?

when i use this—refer to all products. Only GET and POST are supported. from documentation

a screen with (username / and password appears ) i couldn't get what i miss and how to solve

Thanks in advance

You should use the built-in "Storefront REST API" module. Unfortunately, it is not documented yet