When you are in the node area, you can press F to fit the view to all the nodes you have, or press Space -or click the ‘+’ button- then click “Fit View” to do the same.
You can either double click the point you want to change the color of, this will take you directly to its color, or you can right click on the point, and click on the color box.
You can depending on the OS and browser you are using, but a way that should always work is right click on the image you want -> copy image -> click on the nodes area in Karaz -> ctrl+v to paste. This should work on any image you can copy to the Windows clipboard.