Contract Lines

How does the contract lines field work in CRM?  Are the prices you add there recorded anywhere else?  I guess my concern with this is two-fold: I don't want to double count revenue if we have the $30,000 opportunity (for example) and then also the $30,000 contract.  Secondly, I don't want the prices I add for Contract A to be saved anywhere as pricing is different for each client.

Please help!  Thanks in advance.