[ciarain]

Is there a way to create a log file to show which user account logged into my computer and at what time and for how long.

[JLL]

Open Terminal and type last to see who has been logged in in the last few weeks.

[P]

For a longer log, check the files system.log and secure.log in /var/log, as well as the gzipped older versions of them. Easiest way to do that is probably to use Console.app, whcih has links to some of the most common logfiles.

[cybergoober]

You can use the terminal command "zmore" to read the zipped log files.