Hi Kalyani,
Go to your native page from where you want to open a web page -> Definitely there will be button or link to navigate the web page -> make an onClick nanoflow on button/link -> inside nanoflow take an activity openLink-> Pass your web page publish url(https://yourappname-webpagefromnativeapp.sandbox.io) something like this.
Set url inside webpage:-
Go to your web page -> download SetURL widget from marketplace and drag & drop this widget inside web page -> Open SetURL widget & set url anythink(webpagefromnativeapp) & give the access this page to anonymous(If you want to open this page without login manage security according to your need).
Make sure your application should be publish.
Hope you like the an