PEX-A goes on expansion fittings. Usually made by a company called Uponor IIRC. It uses PEX A barb fittings and requires a special tool that is inserted into the PEX, a button is pressed, and the part inside stretches the pipe. You then have a finite period of time to slip the expanded pipe over the fitting before it rebounds to close to original shape/size. I'm not sure whether or not an additional fitting is slipped over to hold it in place. I just did a google search and apparently there is a manual tool for the expansion. also, I believe it does require sleeves to be slipped over the joint after expansion to hold it in place.
The second option is a band that has an bit sticking out that gets squished and thus tightens the ring around the pipe and fitting. It's easy to get the tab into the tool and not have to worry about mis-aligning so much.
Manual tool
Electric tool
PEX-A sleeve
Some people swear by PEX-A and think it is better than PEX-B. I personally like PEX-B. It uses PEX-B barb fittings or push-connect fittings. The latter should only be used in accessible places that you can check for leaks. The barb fittings require the use of a ring to secure the pipe to the fitting. There are two types. One is what I call the wedding band. You have to put the tool over the entire ring and the tool will squish the ring in from all sides to make it clamp down. You have to make sure you have the tool lined up properly to do it right. Well, you have to make sure both tools are lined up properly, but to me its easier to do that with the 2nd version. It fits into the slot easily and then you either us manual cinchers or the electric one.
PEX-B clamp ring
PEX-B Cinch/Pinch ring
Clamp, cutter, and removal tool with a small gauge
Additionally, there is something called a Go/No-Go Gauge that is used to check to see if the PEX-B rings are on properly. The gauge says what size the ring should be and you slide the appropriate divot over the ring. If it goes over it is secured properly. If not, it needs to be redone.
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Editing to add that when searching for the fittings you need to make sure you are getting the right ones for the type of pipe as the barb fittings for PEX-A and PEX-B are different.