If you want to workout in the gym or at home and just buy Dumbbells to do it, this is a way to help you.
To tone your body is to develop and increase your muscle tonus. This means that, even when your not contracting your muscles they have a higher muscle tonus then before.
To gain strength is to develop the ability to support and move higher loads than before by recruiting more muscle fibers and to use them more effectively for a short period of time.
You can either just focus on your Shoulders or add this workout to your weekly routine (in that case you can do it twice a week instead of 3).