problem when draw polygon

hi

i have a big problem when i draw any polygon in opengl

for example:
i used this code for draw POLYGON
GL.Begin(BeginMode.Polygon);
GL.Vertex2f( 0.61, -1.39);
GL.Vertex2f(-0.02,-1.39);
GL.Vertex2f( -0.02,-0.48);
GL.Vertex2f( -0.98, -0.48);
GL.Vertex2f(-1.00,-0.02);
GL.Vertex2f( 0.61,-0.02);
GL.End();

the only way i found to draw polygon on the internet is polygon trianglation but i dont know how to use this

there is a PDF file here https://www.google.com.eg/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0...

explain how to use polygon trianglation plz if any one know the true way to draw polygon plz tell me as soon as possible

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