Know what a triangle looks like and its dimensions. A triangle has three sides, and its internal angles all add up to 180 degrees.
Use a ruler and draw a straight line, however long your paper or canvas will allow. Put your protractor on this line and measure however far you want to create the first angle of the triangle. A 90 degree angle makes a right triangle, less than 90 degrees makes an acute triangle, and more than 90 degrees will make an obtuse triangle. Make a mark where you decide to make the angle.
Draw your second side of the triangle using the mark you made with the protractor as a guide, and connecting it to the first line end to end. You can make this side as long as you like as well.
Draw the third side of the triangle by connecting the opposite end of the first line to the opposite end of the second line. You now have a triangle.