EZ-thru are a type of connector that allow you to put the twisted pairs through the end of the connector so that you don't have to cut them to an exact length because there are holes past the pins at the front of the connector. You can buy a crimping tool that has a blade on the end that will cut the excess off, but these connectors are not as good as the ones that are capped off.
These are the "EZ-thru" type:
Notice how you can push the pairs past the end of the connector pins? You can't do that with the type that are capped off, so you need to measure exactly where to cut it off so that the pairs fit all the way to the end of the connector, but the jacket will go far enough into the connector.
With a non-EZ-thru connector:
You have to measure the exact amount of the (un)twisted pairs to cut off (indicated by the red lines in my diagram) because when you insert them into the connector, the green line indicates the area that is capped off (unlike an EZ-thru connector when you can shove the wires past this point and use a crimping tool that cuts the excess off). As shown you should be cutting enough off so that they will reach to the end of the pins so that they can crimp down into the copper for a solid contact, but also enough to allow for the jacket to reach past the crimp bar that gets pushed down when you crimp the connector (indicated by the orange).
Another thing to note is the T568-A / T568-B standards. A is an older standard but there's no real difference between the two as long as you are consistent when making straight through cables. The US typically uses B for most things, and the only thing I've ever come across was that the cables I use are typically certified using the B standard, so I usually go with B when I make my cables. There may be reasons to use A, but in my experience it's only due to conformity. You don't want to have a network that mixes and matches A and B if they are not prefabricated cables that you might end up re-terminating at some point.