Hi Arpita!
First of all, to set a login page you need to configure it in the navigation of your app:
If an anonymous user tries to access a resource to which the user has no access, the configured sign-in page will be displayed
Here you have more info about authentication widgets: https://docs.mendix.com/refguide/authentication-widgets
For the sign up I recommend you to avoid to use the New Account microflow from the Administration module (inside marketplace modules)
This microflow redirects the user to the Account_New page. However that page has some fields as for example user role. So it’s not correct to give access to the anonymous users to these fields
My recommendation is to create a non persistent entity to capture the information that the user needs to fill as username and password. The rest of the fields you can set them automatically inside a microflow and create the account entity.