Guys, can any one please tell me how I can make the layer one in board layout of eagle a GND plan throughout.

I just can't seem to make that out ?

 

Just draw onto one layer, or set n/a for the layer you don´t want to use if you use autorouter.
To make a ground plane, click the polygon tool, write gnd in the command bar above, then draw the polygon outlines around the board, double click to finish. Use the info tool to see details like isolation distance etc.