Repeat the last command by hitting a single key

Based on the title of my inquiry, you can tell I am a new user to AutoCAD and presently enrolled in the CAD Certificate program at Purdue to learn the program properly. My question is when I am repeating an object such as a line or circle or any other command, I would like the option of hitting a single key, such as a function key, which will repeat the last command without having to resort to a toolbar repeatedly. Another application for this option would be the use of AutoCAD in measuring linear or square feet of space. Any help would be appreciated. Thank You, JAD.

Hit the space bar or the enter key, or the right mouse button (may have to set up as enter in customization).

Kent's solution is the right answer, I've been using the spacebar for over 17 years...many others the right click. Also, Welcome to AUGI! :)

You can also use multiple before a command to make it repeat. I create a command alias of mu for it.