The [Pour Copper] option can be used to automatically add copper shapes to "fill" the spaces between other items on a layer. This is often used, for example, to provide additional shielding by attaching the poured copper to the ground net.
The routines that generate the filled copper areas are obviously quite complex, and there are certain things that you can do to help achieve the best results. One of the most important things is to avoid very short, or very slightly angled, segments in your tracks and shapes. Try and use a reasonable working grid, or use one of the 'segment modes' such as 'orthogonal' or 'right angle' to help you keep segments properly lined up.
You should also avoid putting poured copper areas across the whole design. Instead you should continue to use the powerplane facilities in the plotting to create the necessary 'negative' (and where necessary 'positive') plots needed to generate the filled areas. Filling them yourself can lead to over-large plot files, and can also affect the general performance of editing your designs within Easy-PC itself.