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.
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 a point named C on this perpendicular line by clicking on the point icon and then somewhere on the perpendicular line.
5. Choose the polygon icon in the line drop-down, and then click on A followed by B, C, and A to complete the triangle.
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. Now, only the right triangle ABC is visible.