On a Windows computer you can click on the "start" button and type calculator into the search bar and click on the word "calculator" when it appears. Then, using the mouse or the keyboard, you can enter in an expression and hit enter to get the result.
To access the calculator on a Mac, click on the magnifying glass in the upper-right corner and enter an expression into the search bar and hit enter to get the answer. To access the full desktop calculator on a Mac computer, type the word calculator into the search bar and hit enter. This will bring up the full calculator which acts similarly to the Windows calculator.