There are many areas around your home where concrete products are used and during settling of your home you are likely to end up with cracks that are not structural but should be addressed.
Cracks in foundation walls and slabs are known to allow water infiltration during heavy storms and cracks in your garage slab are unsightly and may result in additional problems.
Filling cracks is a difficult task because you need to apply epoxy throughout the interior of the crack and not just on its surface for best results. The epoxy must be thin enough (low viscosity) to penetrate deeply while not so thin to flow directly out the other side of the piece.
Professionals will use a device able to inject epoxy at up to 6000 psi but during most fills the pressure needed will be much less maybe 200psi at most.
Your ability to seal off the opposite side will also improve results.
For cracks less then 3/8ths of an inch wide you want to use a liquid epoxy. This may require more then one application if you are sealing cracks where the opposite side can not be closed off.
For cracks from 3/8ths to 1/2 an inch you can use a Jell epoxy that will penetrate much deeper into the crack then a thicker paste epoxy.
For cracks over 1/2 an inch wide you may want to consult a professional. Epoxy can be used for larger repairs but the structure may need additional work.
For larger jobs Epoxy can be purchased in Gallons or large Tubes that have mixing injectors with no need to hand mix.
Prepare the Area
Clean the area from all surface contaminants and lose material.
If the surface / interior of the crack is moist then make sure that the epoxy is of a type that can be used in moist conditions.
If a pressurized Epoxy system must be used to inject the epoxy you will need to seal the surrounding surface areas of the crack to provide for attachment of the system.
Fill the interior of the crack to a point 1/2 inch from the surface. Allow the epoxy to cure.
If necessary inject epoxy into any areas that may need refilling.
Once the interior epoxy is cured you may fill the remaining 1/2 inch with a colored paste epoxy.
Note
Remember Epoxy can only be used to seal stabilized cracks it can not be used for structural purposes.
When in doubt always contact a professional and ask advice before you do the work yourself. Hiding a serious problem will only mean it will return.