Construct a Square
To see how GeoGebra works, let's build a figure. Assuming the vertices on a triangle are labeled A, B, and C, you can construct a triangle with a right angle at B by following these steps:
1. In the Geometry window, click on the point icon on the toolbar, and click on any two points in the Geometry window to create and display two points named A and B. {Be careful to not place points to far apart.}
2. Join the two points by clicking on the line-segment icon in the line drop-down on the toolbar and clicking on A followed by B.
3. Choose the perpendicular line icon on the toolbar. Click on the line segment AB and then on point B to draw a line perpendicular to AB at B.
4. Create circle with a center at B and radius BA, the intersection of the circle and the perpendicular line is named C.
5. Repeat steps 3 and 4 to find a perpendicular to BC at point C and create point D.
6. Right-click on the perpendicular line you created in step 3 and uncheck Show Object to hide the perpendicular line from view in the Geometry window.
7. Use the line segment tool and join point B to point C, then point C to point D and point D to point A.
Now, only the square ABCD is visible.