You can use online IDE such as Repl or Codiva. After a while, it is recommended that you switch to a professional IDE such as Eclipse.
Check the latest Eclipse version for you laptop (windows or mac)
Check which java version is required for the Eclipse version to install
Check what java version is installed on your laptop currently, if Java has been installed.
Download and install Java of required version
Download and unpack Eclipse
C. Useful links on Eclipse:
Shortcut keys to add/remove comments, including Java doc comments