The take better pictures page shows how to get good photographs in camera, but almost inevitably some will contain mistakes. These can be corrected using editing software and this article shows how to use the Windows 10 Photos App to correct a few simple and common ones.
Double click your image and providing the defaults on your machine haven’t been changed it will open in the Photos App.
Crooked horizons
These are by far the most common mistake and correction is easy. Under the Crop and Rotate button you can rotate the picture around with the slider, lining up the horizon with the grid that appears.
Composition
This can usually be corrected by using the crop function, moving the boundaries of the picture to suit what you want. 
Clicking on the picture brings up a rule of thirds grid to help you and you change what you see by moving the corner markers over the picture. You can move the crop box over the picture by clicking on it and then dragging the mouse the same time but note this only works if you have already cropped into the picture itself.
Lighting and colour
Various controls can be found under the Adjust heading. Rather than lots of words in this article the best way to see what they do is to play with them on a sample image.
Some of the controls have a little right pointing arrow on the left-of their name, clicking on that reveals controls to handle contrast, exposure, highlights, shadows, tint and warmth.
In some photos whatever you do it still looks wrong, perhaps due to a colour cast or something else wrong with the colours. More sophisticated editing software can deal with that, although there is a learning curve, but also consider conversion to black and white by moving the colour slider fully left. It can be surprisingly effective.
An important point about saving
The.jpg file format, which are almost certainly using, by design compresses and therefore loses image data each time an image is saved. To avoid this, make all your changes and save only once.
Always save changes to copy and not the original, as in that way you always have the original as taken if you want to alter something else.
Less is more
It is very easy to overdo editing and end up with something that looks unnatural or worse very obviously processed. In some cases that might be what you want, to produce an artistic effect, but in most other cases only make subtle changes and no more.
Monitor and printer colour accuracy
This is a subject in itself, since getting what you see on-screen to match what you see on the print or on a different display device is unfortunately less than straightforward. Professionals use complex calibration equipment and software although there are things that you can do without it. Microsoft Windows 10 has some simple colour and calibration controls:
- Monitor – Settings> System> Display> Display adapter properties> Colour management.
- Printer – colour management depends on the driver provided by the manufacturer – Settings> Devices> Printers and scanners, then click on your printer and open the Manage tab.
You can then play with these manually to try to get the best match possible, although be warned it’s not usually a quick process and you will use a fair bit of ink (or toner) and paper!