Hello @dkcbk !
This : $ cp *.y[a]ml /some/dir will not copy the .yml files because it will expect "a" in the extension.
Try this and you can copy all the files having similar extensions like .jpeg or .jpg , .yaml or .yml or likewise :
Actually, this will work just fine, because star matches 0 to any number of characters (this also assumes no other files, such as *.yxml, exist):
cp *.y*ml /some/dir
cp *.yml *.yaml /tmp
Other answers here give you the same thing, but the copy command is capable of copying multiple files, when you have a list of multiple files or file types, the last argument on the line is the directly location where you want to copy the files.
The answer @Tracy_Baker gave you is good too, but as he mentioned it will get other files if they happen to exist. The command above gives you just yml and yaml extenstions and won't get any other files.