Reset all settings?
Erase all content and settings?
Reset network settings?
(keyboard is obvious)
(homescreen is obvious - i hope)
Reset location and privacy?
Reset all settings does just that, resets all settings back to default. Example, if you turned Bluetooth off and changed around a bunch of notification centre settings, they would retun to their original state.
Erase all content and settings one ups the above by erasing the entire device. This will put it back through the initial setup assistant and everything. No content will remain on the device afterwords.
Reset network settings erases all saved network configurations such as wifi networks and passwords, VPN settings, and APN settings.
Keyboard and home screen are obvious yes.
Reset location and privacy resets all saved information about frequent locations and privacy. Apps will ask you if they can access your private information again after doing this reset option.
If someone told you to do just a "reset" you can do this by holding down the sleep/wake button and home buttons simultaneously. This forces the device to shutdown. Keep note that it should only really be used if the device is frozen or otherwise unresponsive. It's always better to properly shutdown if you can instead by holding just the sleep/wake button and sliding to power off.
Also, a great place to read up on stuff like this is in safari on the device itself, if you go to your bookmarks you should see an "iPhone User Guide". Top left corner has three lines with what look like bullet points. This will give you a good visual breakdown of the user guide. A search in the top right for reset brings the above info.
