Fixing cracks and holes in old concrete can become a very big chore. You can't just fill in the cracks and expect them never to come back. Instead, over-pour your existing concrete with new concrete to repair and strengthen the entire structure. Use a bonding adhesive to ensure the new concrete sticks to the old surface.
Remove all debris from the old concrete. This can be done with any type of tool that scrapes up the flaky concrete. A flat shovel works well.
After you built your forms and placed them alongside the concrete, apply a thin coat of the bonding adhesive. Use a paint roller to apply if the adhesive didn't come with its own brush or applicator.
Mix, pour and smooth your concrete out on to your old concrete slab. Use a wet trowel to perfectly smooth the top once all the concrete is on.
Allow the concrete to dry for between 17 to 24 hours to make sure the best seal is achieved. Remove the forms after the proper period of drying has passed.