Please note that the chainmail may have an oil residue on it from the manufacturing process. This can be removed with soapy water but you shouldn't wear the mail over nice clothing.
Chainmail does not stretch so it cannot be put on like a normal shirt. The best way to put it on requires two people. The person who is going to be wearing the shirt should kneel down with his arms pointed to the ceiling and someone else needs to gently lower the shirt onto him. To remove the shirt simply bend over and touch your toes and wriggle a little and it will come off. If you try to put it on normally you will stretch the metal when wriggling your elbows in and that can pull rings apart, especially with aluminum mail.
It is important when holding the shirt that you grab it by handfuls, holding onto a single ring or a few rings can cause the weight of the shirt to pull those rings apart.
If a ring falls off or pulls apart you can repair it relatively easily. All you need is two pairs of needle-nose pliers and the missing ring, simply examin the other rings on the shirt or coif and see how they fit together, then knit the missing ring back into place and use the pliers to bend it closed. If you're missing the ring you can make a new ring using wire of a similar type.