If you remember drawing three-dimensional cubes and rectangles in the margins of your notebook paper when you were bored during class, you can draw a triangular prism. The same mechanics that applied to squares and rectangles apply to the triangle; the only difference, other than working with three sides instead of four, is that if you draw the prism standing on its end, you may have to be a little more careful which points you're joining up.
Draw one triangle on a sheet of paper. Use a ruler so that the lines are straight. You can make a triangular prism out of any shape of triangle, so draw whichever type you want. Right triangles have one angle of 90 degrees; equilateral triangles have three equal sides and angles; isoceles triangles have two equal sides and angles; and you can also draw other triangles that have all different sides and angle measurements.
Draw an identical triangle off to the side. Imagine the first triangle is in a square; draw the second triangle at one of the corners of the square. Technically you can place the second triangle on a line directly horizontal or vertical from the first, but drawing it off on a diagonal results in a cleaner picture.
Draw a straight line from the top point of the first triangle to the top point of the second triangle. Draw lines connecting the bottom left points of the two together, and the bottom right points together. The result is a triangular prism.
To draw the prism standing on one end, draw the second triangle directly above or below the first. The procedure to connect the two is exactly the same as in the steps, but you can see that one side is now cramped and harder to see. That can be a little more difficult for a first drawing, especially if you are using graph paper, which adds its own lines into the visual mix. The West Deptford School District in New Jersey has tips on how to add depth perception to the drawing: Draw a straight horizontal line above the first triangle and place a dot on the line somewhere. Connect all three points of the triangle to that one dot. At some point along the ribbon of lines between the triangle and dot, draw additional lines that mirror the first triangle to create a second triangle -- except place the points of the triangle on the lines running between the dot and the first triangle.