Thanks for the follow-up :-)
1. Once the user is logged in successfully, he/she must be redirected to payment page.
What you’re referring to is what s2Member would consider a Billing Modification.
If you’re using Pro Forms, you’ll want to use a Billing Modification Form, which upgrades an existing User/Member to Membership Level #1, 2, 3, 4 (whatever you like). A Pro Form for Billing Modifications will not work unless an existing User/Member is logged in, and that’s what you’re describing here. It’s fine if they’re not paying you yet, s2Member is still Modifying them, and we are not registering someone new in this case.
See: Dashboard -› s2Member® -› PayPal® Pro Forms -› Billing Modification Forms
2. Payment page will be accessible to only those who’re already a member of this site., not to everyone.
You would protect this Page using s2Member’s Page Restrictions, and require Membership Level #1, or whatever you require in order to access this Page that contains your Pro Form for Billing Modifications. This way it’s not available for public access, an existing User/Member must be logged in before they access it.
See: Dashboard -› s2Member® -› Restriction Options -› Page Access Restrictions
3. Also, please let me know that how can I create a payment/paypal page where I will take payment information from a user.
The instructions I provided above should get you there. As for the redirection itself, you will need to get creative, because you need to do this conditionally (i.e. only redirect if they are NOT a paying customer yet).
Here Is One Idea For You (Multiple Login Welcome Pages)
See: Dashboard -› s2Member® -› General Options -› Login Welcome Page
Use one of s2Member’s Replacement Codes here, and type your own Login Welcome Page URL.
Now create Login Welcome Pages for each Membership Level you’re selling (including Membership Level #0, for Free Subscribers). For instance, you might have the following Pages.
http://www.example.com/0-account-page
This Page would contain the Pro Form for Billing Modifications, along with any other details you’d like to publish on this Page. So this is the redirection page you were asking for. This is where a new Free Subscriber would be taken, upon logging into your site (if they are still at Membership Level #0, a Free Subscriber).
http://www.example.com/1-account-page
This is the Login Welcome Page for paying customers that are at Membership Level #1. Put whatever you like here. For instance, links to the content that is available them; now that they’re a paying customer.