Here you assign the layer a name. This does not have any functional significance: it is simply a convenience to help you remember the role you intended the layer to play when you created it. By default, the name "New Layer" is used. If a layer with this name (or whatever name you choose) already exists, after you hit the "OK" button, a number will be appended to the name in order to make it unique, i. e., "New Layer#1".

Here you set the dimensions of the new layer. When the dialog appears, the values are initialized to the dimensions of the image. You can change them, and if you want to use units other than pixels, you can get them using the Units menu to the right. You can't set the position of the layer within the image here, but you can always move it after it has been created.

Here you have four options for the solid color that will fill the layer: the active Foreground color, the active Background color, White and Transparency