If the ball will not stay together, you will need to add more water. Mix the concrete by adding very small amounts of water. It may seem to crumble at first, but as you continue to add water it will start to look like a thick mud, turning a medium gray color. The concrete takes on a plastic-like, shiny sheen. When you begin to mix the components of concrete, you can use a wheelbarrow or any flat waterproof surface that can be hosed off at cleanup time, such as a sheet of plywood.
Most concrete mix comes with their mixing directions written in ratios.
An easy way to decipher these, is to measure each item in a bucket. Use the straight edge of your shovel to level off the bucket, so each bucketful is the same amount. Using a concrete hoe to mix the components, rolling one item into the other. If the mixture is a little dry make a little pond in the center of the mixture and add water gradually to the mix. To test the fully mixed batch, smack the pile flat with the back of the shovel.