Mechta,
Info on Dynamic Named Ranges can be found
HERE.
If you want to extract 20 sheets worth of data to one sheet (along the lines of a Dashboard presentation), you could highlight your data, right click/copy. Go to your main sheet, right click a suitable cell, and Paste Special/Paste Link from the contextual menu that springs up. This means that when you input a figure on a data sheet it will automatically be mirrored in your main sheet. So no tedium there to worry about.
Other EXCEllent sites (did you see what I did, there?)
HERE, and
HERE.