Dispposal Account Rules

Hello,

I am having trouble setting up my Account Disposal Rules. First, I am somewhat unsure of the nature of these accounts. We currently do not have accounts properly set up for these and will have to add them into our chart of accounts. I beleive understand the Net Book Value account, but am having trouble with the clearing account and proceeds accounts. Can someone explain the nature of these? Also, how should the level of detail work on these. Should the Gain/Loss on Disposal of Asset not be posted to and just have the 3 disposal accounts roll up into it? I was also thinking of