You have to learn all the basic knowledge about soil, aspect and plants. Correspondence courses are available through the Royal Horticultural Society, and many universities and colleges offer excellent courses. To my mind, though, the best experience you can get comes from working with an experienced gardener or garden designer in order to learn as much as possible on the job. Oak trees cause shady, dry conditions beneath their canopy. For some permanent colour try painting any woodwork, such as trellises and sheds, with a light coloured paint.
Glazed pots are available in a range of colours and sizes and can look stunning on their own.
Although we do need to park all the family cars on it, it currently consists of several different areas of concrete, most of which is disintegrating, and tarmac patches. I would like to completely replace the whole area with gravel and incorporate a few shrubs around the borders, but don't know where and how to begin. The first step is to get rid of the concrete. Use the iron bar as a lever under the concrete and then hit the concrete on top with the hammer. This will break it up into manageable pieces.