The step starting
Create a SIP account
Is vauge to say the least.
Example, the sentence
Copy one of the device configs in the SIP configuration file sip.conf and change for one of your phones. You should only have to change the device id.
Their is not a procedure or example on how to do this other then to what? Uncomment the section applicable to you? The device id - how is that determined across vendors/phones?
Below it offers a glimmer of help by mentioning:
If you want to learn more on how to get this configured, read the introdcution articles referenced to on the Asterisk page, the bottom half.
Instead of giving a URL or reference it basically says "waste your time looking in this area. Don't look for headers, urls or big flashing pieces of text just look"
If this question can be redone it would really make this help page shine.