click the copper outline, change its net at the right-hand panel.

I think you got me wrong What I'm trying to say is how the copper layer connect to the power supply?

@seetcas, Your question is unclear. Are you asking about: 1. adding a Copper Area to create a ground or supply plane area on a 2 layer PCB or; 2. how to define one or more of the inner layers to be used as ground and power planes in a multilayer PCB?

Ok let me clear that for you Copper layer for GND If I'm making a copper layer GND then there should be a physical contact between my supply source GND and copper layer GND, am I right? If so where is that contact located?

Still not clear if you are talking about making a copper area on a layer or using the feature that allows you to define an inner layer as a ground or power plane. Either way you need to set the net name to be the same as that of the net you want the copper area to connect to (GND or VCC etc.). If there are any pads on the same net surrounded by the copper area then when you do shift+B to rebuild the copper, it will automatically connect to the appropriate net. Or run a track from the nearest pad into the copper area. You may need to add vias to connect SMD pads from other layers. For  dedicated copper layers then the same rules apply but you may need to add via to connect to the same net on other layers. Build yourself a simple test project and play with the tools to get CD the idea of how EasyEDA works before you launch into a bigger project. :)

@andyfierman Well, You got to the point " If there are any pads on the same net surrounded by the copper area then when you do shift+B to rebuild the copper, it will automatically connect to the appropriate net" Thank you very much now I understand how that works, One more question if I make top layer as GND and bottom layer as VCC Will component on top layer still be able to connect to vcc on bottom layer with out any conflict? and vise versa

"Will component on top layer still be able to connect to vcc on bottom layer with out any conflict? and vise versa" As already explained above: You may need to add vias to connect SMD pads from other layers. For  dedicated copper layers then the same rules apply but you may need to add via to connect to the same net on other layers. Anywhere you have through hole components then you do not need to use a dedicated via as through-plated multilayer component pads connect to all layers.

@andyfierman Thanks for making things clear