I applied for early access of Apply Pay Later and got approved but it is not clear where I can use it as a payment option. Is it only for online purchases where Apple Pay is an option to check out?
Apple Pay Later can only be used online and in apps that accept Apple Pay. See the following from How to set up Apple Pay Later - Apple Support
You can use Apple Pay Later at participating online and in-app merchants that accept Apple Pay. 
Want to pay for items at Ross store right now
please how do I do thst
Can I use Apple Pay Later for store purchase of goods and service if I use Apple Pay?
