The proposal popup windows looks just like the regular JDT popup.

When the content assist proposal is selected, CompleteClipse will calculate the best variable to pass in as an argument.

CompleteClipse is also very good at "delegation" completions, where you pass the work on to another method with a similar signature.

If you have the 'no fill' [NF] option on, you will see two choices for every method with parameters.

If you select an [NF] proposal, it works just like regular code completion.

Here is a quick look at the preferences.