Given the side lengths 6, 8 and 12 you have to draw a triangle and then classify it.
First step is to draw the triangle:
I'll name the triangle ABC and the segments will be
AB=6
CA=8
BC=12
Select one of the line segments as a base, for example segment AB
Using point A as the center and with help of a compas, draw an arc with radius 12
Then using point B as the center, draw an arc with radius 8
Where both arcs intersect, is the location of point C. Once this is determined you can draw the triangle.
For the triangle ABC, the red circle has a radius of 8 units and the blue circle has a radius of 12 units.
As you can see, the angle m∠BAC is greater than 90 degrees, this means is an obtuse angle.
Since the larger inner angle is obtuse, you can classify this triangle as an obtuse triangle