How do I connect an air compressor to blow out my sprinkler lines?
What I usually do to blow out lines is just use a simple hand held blow gun fitting for the air line. You can buy one that has a rubber end that fits inside the garden hose valve. This usually fits well enough that I don't need to do anything special.

When that is insufficient, then I do have a short pigtail (a one foot long piece) of hose with a regular air line connector at one end, and at the other end a female garden hose nozzle. You could probably just chop off the end of an old piece of regular water hose, since it will already have the male garden fitting on it. At the other end, I would buy a barbed fitting of the right diameter that would allow me to connect to a 1/4 NPT threaded connector. Then just screw on a ball valve to turn the air on from the compressor when you want it, and to that, screw on a male air line connector. A GOOD hardware store will have all of these things.

The nice thing about a blow-out tool like this is it does not need to take any serious airline pressure because the end of the line you are blowing out is essentially open ended. So a simple piece of garden hose is entirely sufficient. You might even temporarily reduce the regulator on the compressor to about 40 psi to avoid damaging anything from overpressure.

If you don't know how to make this up, then I'd go to a local hardware store and ask for help. Tell them what you need. (Print out this response if necessary.) Go to a GOOD one, not to the big box stores like Home Depot. Find one of those stores where the person running it knows what they have in the store and where to find it, and they know how to use what they sell too. When you do find such a hardware store, support them with your business on a regular basis.