1. There's no need to make two topics for this.
2. I have no idea what you're talking about in your first post. Do you mean that you closed the tab in the red rectangle below?
3. Checkerboard material means that it's transparent, so if this is a sprite you're working on, there's no point to adding a white background. But, if you really want to add a white background, you can click "New Layer" and add a white layer. Then, all you have to go to stack and lower the current layer.
4. You can resize the layer you are working on with the scale image option.
5. Please use capital letters at the start of a sentance, and only one punctuation point at the end.