Apple have made the setup very easy. Just follow these steps:
1. Go to the "Settings" app.
2. Click on "Accounts & Passwords"
3. Click on "Add Account"
4. Click on "Other" at the bottom of the list
6. Click on "Add CalDAV Account"
7. Enter the following details:
Server: rostersms.com User Name: Your RosterSMS.com User Name Password: Your RosterSMS.com website password Description: RosterSMS (or any label you like)
8. Click "Next". You should see ticks briefly appear next to your entries as the iPad confirms your calendar setup. Then the following screen will appear.