 For this, you'll need a concrete resurfacer. After a good cleaning, you'll need to fill in any cracks, pits, or spalled areas with a small batch of the resurfacer. Just spread it on with a trowel. Then you can mix up a larger batch and spread it over the whole area with a squeegee about a sixteenth to a quarter inch thick. If you want a non-slip surface, you can drag a fine bristle broom over it after a few minutes to create a textured finish.