Q: how do I wipe all my information from my iPhone 4S before I sell it?

You'll want to connect it to a computer and restore the software using iTunes.

For your second question; yes! You can do the backup through iTunes as well.

http://support.apple.com/kb/HT1414?viewlocale=en_US - How to Restore

http://support.apple.com/kb/HT1766 - How to Backup (both iTunes and iCloud)

Make sure you do the backup before you do the restore.

Back all required data best to use iCloud as that is accessible "anywhere " if you do not have the iTunes PC /MAC with you in US

Settings >>>General>>>reset>>>erase all content and settings

and remove sim

Before you wipe, make a backup on iTunes as well as iCloud.

Wipe iPhone/iPad/iPod touch clean

Switch off iMessage in Settings > Messages

Switch off FaceTime in Settings > FaceTime (iPod touch 4th Generation or later, iPhone 4 or later and iPad 2 or later)

Delete iCloud in Settings > iCloud > Delete Account

Finally Settings > General > Reset > Erase All Content and Settings.

Un-register your device: https://supportprofile.apple.com

Now you can sell/give.

Here is the "official" document from Apple:

http://support.apple.com/kb/HT5661

how do you remove the sim?

Got it

iPhone and iPad: How to remove the SIM card 

http://support.apple.com/kb/HT5163?viewlocale=en_US&locale=en_US