Use the "Move this for different triangles" button to move the vertices of the triangles around. See if you notice a pattern in how the angles are releated and with the total sum of the triangles.
What pattern did you notice about the angles in the triangle?
Add the angles of the triangle together. What is the sum?
If you move 1 vertex around, can you make the other two angles larger at the same time?
Click on the "Move" button. What did you notice happen with the angle and exterior angles(those that form a linear pair with the vertex)?