If my home network is down or if I am traveling, how do I use my phone to access the internet. Basically how would I tether it to my other devices.
If you have Android 2.2, the functionality is built in so there usually is no need to install a separate app. Just go to: Settings > Wireless & networks > Tethering & portable hotspot.
However, depending on your phone, it is possible that your carrier has locked down this functionality. If this is the case, you can either root your phone and install a clean Android 2.2 such as Cyanogenmod, or you can call your carrier and pay their fee to enable it.
Unless you are paying for the service from your carrier, you can root your phone and install a tethering app from here. If you would rather not root your phone, you could go with PdaNet from the Market.