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new serverFrame()

    s = new serverFrame()

That is really all there is to it :-) See the User's Guide 4.1 and 4.2 for an introduction on serverFrames.
An alternative method of creating a serverFrame is the win method "addServerFrame()". There really is not much difference between the two. If a serverFrame has been created within a window, it wil be submitted with all other serverFrames in that window by "win.submit()" and the leftmost button on that window will turn red while any of its serverFrames is still being processed.