You'll see a screen or two of terms and conditions. You're required to agree to them in order to use your iPhone, so go ahead and agree.
Once you've done that, you'll have a pair of options related to iCloud, a free web-based service Apple offers to its customers that allows you to do many things. Generally speaking, I recommend using iCloud since it allows you to do the following:
- Use Find My iPhone
- Redownload Purchases from iTunes
- Use PhotoStream to store and access photos online
- Store and access Pages, Keynote, and Numbers documents online
- Backup your iPhone data and restore from backup over the Internet
- Use your iCloud as a central account for your calendar, contact, and email and sync them to all iCloud-compatible devices
- Use iTunes Match
Your iCloud account will be added to the Apple ID that you entered or created in the last step.
To enable iCloud, slide the button to On, or leave it off and tap Next.
Next, decide where you want to backup your iPhone. If you choose iCloud, your data will be backed up to iCloud each day via Wi-Fi. This has a number of advantages--your data isn't on your computer, so a hard drive crash can't lose it; you can restore over the Internet (as seen in step 3)--but you may prefer to backup your iPhone to your computer each time you sync.
Tap on the option you want and then tap the Next button to continue.