Path to...

The ‘path to’ command will give you the location of a number of ‘blessed’
directories, including Application Support.

Note, if you want the system Application Support directory (typically
/Library/Application Support/", remove the ‘from user domain’ part of the
path to command. The ‘user domain’ element makes sure you get the user’s own
/Library path.

OS version: OS X

set appSupportPath to path to application support from user domain
tell application "Finder"
    make new folder at appSupportPath with properties {name:"MyFolder"}
end tell