My first openGL program! Rainbow - part 1

I am finally taking graphics classes and I am so excited!  We haven't had any real assignments yet, we just had to run a sample program on OpenGL and see "Hello Triangle!"  I tried playing around on my own today to familiarize myself with this program I will be using a lot.  I wanted to make a rainbow today.  It's not quite a rainbow yet but it's trying.

Here is my source code so I don't lose it!  And with comments that hopefully will clear things up for myself when I look at it down the road.

void display()
{
glClearColor(1,1,1,1); // made the background white
glClear(GL_COLOR_BUFFER_BIT); // not sure what this does but it doesn't clear properly without it

glBegin(GL_LINES);

// draws red part
glColor3f(1.0, 0.0, 0.0);
    glVertex3f(-1.0, 0.5, 0.0);
glVertex3f(0.0, 0.55, 0.0);
glVertex3f(0.0, 0.55, 0.0);
glVertex3f(1.0, 0.5, 0.0);

// draws orange part
glColor3f(1.0, 0.5, 0.0);
glVertex3f(-1.0, 0.45, 0.0);
glVertex3f(0.0, 0.5, 0);
glVertex3f(0.0, 0.5, 0.0);
glVertex3f(1.0, 0.45, 0);

// draws yellow part
glColor3f(1.0, 1.0, 0.0);
glVertex3f(-1.0, 0.40, 0.0);
glVertex3f(0.0, 0.45, 0);
glVertex3f(0.0, 0.45, 0.0);
glVertex3f(1.0, 0.40, 0);

// draws green part
glColor3f(0.0, 1.0, 0.0);
glVertex3f(-1.0, 0.35, 0.0);
glVertex3f(0.0, 0.4, 0);
glVertex3f(0.0, 0.4, 0.0);
glVertex3f(1.0, 0.35, 0);

// draws blue part
glColor3f(0.0, 0.0, 1.0);
glVertex3f(-1.0, 0.3, 0.0);
glVertex3f(0.0, 0.35, 0.0);
glVertex3f(0.0, 0.35, 0.0);
glVertex3f(1.0, 0.3, 0.0);

// draws purple part
glColor3f(1.0, 0.0, 1.0);
glVertex3f(-1.0, 0.25, 0.0);
glVertex3f(0.0, 0.3, 0);
glVertex3f(0.0, 0.3, 0);
glVertex3f(1.0, 0.25, 0);

// every begin needs a matching end
// every specific shape needs a separate begin, end (can't draw triangles in between this, for example)
glEnd();

glutSwapBuffer(); // not sure what this does but without it, the entire image becomes white
}

int main(int argc, char** argv)
{
glutInit(&argc, argv); // still worked when this was commented out.. hmm..
glutInitDisplayMode(GLUT_RGB|GLUT_DOUBLE|GLUT_DEPTH);
glutInitWindowSize(600,600);

glutCreateWindow("not a rainbow but i can still pretend");
glutDisplayFunc(display);

glutMainLoop(); // no compiler errors when this was off but it just closed after a second
}

I realize it could have been done a lot.. better..  But I'm gonna call the beginner card on this one.

Here it is haha:

Poor rainbow.  It's struggling