The Chord Tools
You'll see chord tools above the keyboard if you're doing an exercise in identifying chords in a chord progression. A writing activity might also display a tool you can use to create chord symbols.
In a chord progression ear training exercise you'll normally see chords listed by the Roman numeral - it depends on how the activity designer has set up the exercise. Here's an image from Level 2 of Chord Progression Ear Training:
To enter one of these provided chords in the music, click on the appropriate chord box and then click in the music where you want that chord to go. In a chord progression exercise there will be a series of empty numbered boxes in the music window - after clicking on the name of the chord you're choosing you'll click in one of those boxes to place the chord at that location. If you change you mind, you can just choose a different chord and click in the same box again - the new chord name will replace the old one.
When you complete the exercise you'll be shown the music (assuming the instructor has allowed that) and you'll see any wrong choices circled in red, and the correct answers printed underneath each box:
Creating chords with the chord tool
Click on the chord tool and you'll see a window in which you can specify the notes (up to six) and the name of a desired chord. The name can be anything you like. Then click in the music where you want the chord symbol to appear. Once a chord symbol has been placed in the music you can select it with the arrow tool and drag it left or right. The Spreader and Shrinker tools can also be used in the chord layer to move chords left and right.