Q: is there a site called iCloud.com

Yes, yes it is. http://icloud.com is Apple's website for all iCloud services, including Activation Lock.

If you have not done so follow the support article linked below to reset the iPhone back to factory condition so the next owner can set it up as their own.

What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support

You can restore it from icloud.com if you wish, and remove Activation Lock from it as well.

Find My iPhone Activation Lock - Apple Support

iCloud: Activation Lock

Turn off Find My iPhone Activation Lock - Apple Support

Please read the articles above and understand that if you do not correctly remove Activation Lock, the next owner will not be able to use the iPhone you are selling them.

If you have set up 'Find My iPhone' then anyone who purchases will find the phone bricked when the reset or update it, and only you can unlock it. Basically you need to sign out of iCloud altogether, for which you will need your password to turn of 'Find My iPhone'. You should then reset the phone to factory settings. Please see What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support