Patching asphalt surfaces is actually a very manageable DIY project. Even if you don't have any experience working with asphalt, you will probably find that asphalt patch easy to work with. This article explains what products and tools you need to patch asphalt like a pro. It also runs you through the process, and should help you understand important differences between asphalt patch and sealcoat.
Patch Before Adding a Sealcoat Finish
First of all, if you have holes, cracks, and other voids in your asphalt, you need to patch them with asphalt patch before applying a sealcoat finish. You can apply a sealcoat on top of your asphalt, after all of the damaged areas are patched. However, adding a sealcoat directly on top of your existing concrete, without patching the damaged areas, is going to be counterproductive. Basically, sealcoat is similar to applying a new coat of paint of your asphalt. It won't protect or reinforce any significant holes or cracks in the surface.
Using the Right Type of Patch
It is also extremely important that you have the right type of asphalt patch. For most patch jobs, especially on residential properties, cold formula patch is all you need. Most large asphalt jobs use hot formula asphalt. But, this is usually only used in the original pouring of asphalt and for major repairs to be asphalt surfaces. Cold formula patch is very convenient and easy to use. It comes premixed, and you can find it in large tubs or smaller caulk tubes. Both can be useful. The caulk tubes are great if you have narrow, but deep cracks.
All you really need to apply asphalt patch is the actual product and a rubber squeegee. The trick to patching asphalt surfaces is to you fill in the cracked and also spread it on to the top of your walking surface. That is, you want to completely cover the damaged area, and not just fill in the crack. This is were having the squeegee will be important. You can use the squeegee to shape the edges and make sure there are no ridges or seams that stick up.
Now that your asphalt is properly patched, you can start to think about if you want to apply a sealcoat. Adding a sealcoat finish on top of an old piece of asphalt that is fully patched, can basically make it look much newer and blacker.