Help with pop up window/2nd sheet within workbook

I would like for a rate calculator I've put together in Sheet 2 to pop up
when button clicked Sheet 1. After the dimensions are keyed in, I would
like the calculated figure to populate a cell with-in Sheet 1 when button to
return to Sheet 1 clicked.

1 issue is I would like the user to have the option of keying in directly to
figure if already known or have the calculated figure from Sheet 2 populate
upon return.

This figure is the base for other calculations with in Sheet 1.

(Minimum experience with Macros/Visual Basic - Mainly 'Macro Recorder')

Your trusted assistance greatly appreciated.

Steven