Just a couple of things:
If you were asking what shadow is, then it is possible you have not had that much coaching. The primary reason for performing shadow badminton is to develop quick, balanced, efficient footwork. Before starting to incorporate shadow into your training you must get a coach to show you how to move properly, better still get a video lesson. If you are not practicing correct footwork you will groove any faults and find it very difficult to change them later on.
As well as helping with footwork shadow helps with fitness and leg stregth. You can vary the pace of your movements around the court. If you run as fast as you can with large leaps and lunges this will work on your plyometric strength, but don't do it for longer than about twenty seconds and take a long rest afterwards. If you want to work on perfecting technique you should perform very slow shadow.
The second thing is hitting against the wall. This is potentially a great way of developing your racquet speed, good for defence, and the strength of your tap action. It is also good for people who take large swings at the shuttle when they should be taking small ones, as a large swing will not allow you to keep the shuttle going.
However, a trap that is easy to fall into when hitting against the wall is looking in the wrong place. You should be looking at the shuttle at all times - watch it hit the strings every shot. When hitting against the wall it is very easy to look at the wall and use judgement and peripheral vision to hit the shuttle. This is about the worst habit you could develop. Take a look around at the less able players you know - how many of them defend a smash by watching the shuttle onto the strings. There is a reason why they don't get many smashes back.