well I am able to draw and move the plane and shoot bullets and move the enemy plane from the top to the bottom of the screen. here is my code so far.

#include <freeglut.h>
#include <iostream>
#include<SOIL.h>

using namespace std;

GLuint textureBrick[8]; 

float move_plane = 0.0f;
float up = 0.0f;
float down = 0.0f;

GLuint loadTex(const char* texname)                                    
{
	/* load an image file directly as a new OpenGL texture */
	GLuint texture = SOIL_load_OGL_texture
	(
		texname,
		SOIL_LOAD_AUTO,
		SOIL_CREATE_NEW_ID,
		SOIL_FLAG_POWER_OF_TWO
	);
	return texture;
}

void init()
{
	textureBrick[0] = loadTex("C:\\Users\\Owner\\Desktop\\plane.png");
	textureBrick[1] = loadTex("C:\\Users\\Owner\\Desktop\\bullet.png");
	textureBrick[2] = loadTex("C:\\Users\\Owner\\Desktop\\enemy.png");
}

void timer(int)
{
	down--;
	if (down <= -160.0f)
	{
		down = 0.0f;
	}
	glutPostRedisplay();
	glutTimerFunc(1000.0 / 60.0, timer, 0);
}

void renderScene(void)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glPushMatrix();
	glEnable(GL_TEXTURE_2D);

	glBindTexture(GL_TEXTURE_2D, textureBrick[2]);
	glBegin(GL_QUADS);
	glTexCoord2f(0.0f, 0.0f);
	glVertex2f(-10.0f, 100.0f + down);
	glTexCoord2f(1.0f, 0.0f);
	glVertex2f(10.0f, 100.0f + down);
	glTexCoord2f(1.0f, 1.0f);
	glVertex2f(10.0f, 80.0f + down);
	glTexCoord2f(0.0f, 1.0f);
	glVertex2f(-10.0f, 80.0f + down);
	glEnd();

	glBindTexture(GL_TEXTURE_2D, textureBrick[0]);
	glBegin(GL_QUADS);
	glTexCoord2f(0.0f, 0.0f);
	glVertex2f(-10.0f+move_plane, -80.0f);
	glTexCoord2f(1.0f, 0.0f);
	glVertex2f(10.0f+move_plane, -80.0f);
	glTexCoord2f(1.0f, 1.0f);
	glVertex2f(10.0f+move_plane, -100.0f);
	glTexCoord2f(0.0f, 1.0f);
	glVertex2f(-10.0f+move_plane, -100.0f);
	glEnd();

	glBindTexture(GL_TEXTURE_2D, textureBrick[1]);
	glBegin(GL_QUADS);
	glTexCoord2f(0.0f, 0.0f);
	glVertex2f(-2.5f+move_plane, -75.0f+up);
	glTexCoord2f(1.0f, 0.0f);
	glVertex2f(2.5f+move_plane, -75.0f+up);
	glTexCoord2f(1.0f, 1.0f);
	glVertex2f(2.5f+move_plane, -80.0f+up);
	glTexCoord2f(0.0f, 1.0f);
	glVertex2f(-2.5f+move_plane, -80.0f+up);
	glEnd();
	
	glPopMatrix();
	glutSwapBuffers();
	glDisable(GL_TEXTURE_2D);
}

void ChangeSize(GLsizei w, GLsizei h)
{
	GLfloat aspectRatio;
	if (h == 0)
		h = 1;
	glViewport(0, 0, w, h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	aspectRatio = (GLfloat)w / (GLfloat)h;
	if (w <= h)
		glOrtho(-100.0, 100.0, -100.0 / aspectRatio, 100.0 / aspectRatio, 1.0, -1.0);
	else
		glOrtho(-100.0*aspectRatio, 100.0*aspectRatio, -100.0, 100.0, 1.0, -1.0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}

void shoot()
{
	up++;
	if (up >= 175.0f)
	{
		up = 0.0f;
		glutIdleFunc(NULL);
	}
	glutPostRedisplay();
}

void handleKeypress(unsigned char key, int x, int y)
{
	int animate = 0;

	switch(key)
	{
	case 27:
		exit(0);
		break;
	case 32:
		animate = !animate;
		if (animate)
			glutIdleFunc(shoot);
		else
			glutIdleFunc(NULL);
		break;
	}
	glutPostRedisplay();
}

void handleSpecialKeypress(int key, int x, int y)
{
	switch (key)
	{
	case GLUT_KEY_LEFT:
		move_plane--;
		if (move_plane <= -125.0f)
		{
			move_plane = -125.0f;
		}
		break;
	case GLUT_KEY_RIGHT:
		move_plane++;
		if (move_plane >= 125.0f)
		{
			move_plane = 125.0f;
		}
		break;
	}
	glutPostRedisplay();
}

int main(int argc, char **argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
	glutInitWindowPosition(400, 300);
	glutInitWindowSize(800, 600);
	glutCreateWindow("Combat");
	glutDisplayFunc(renderScene);
	glutTimerFunc(1000.0 / 60.0, timer, 0);
	glutReshapeFunc(ChangeSize);
	glutKeyboardFunc(handleKeypress);
	glutSpecialFunc(handleSpecialKeypress);
	init();
	glutMainLoop();
	return 0;
}