How to use BeginMode2D() and Camera2D()

[TheAngriestCrusader]

I can't seem to find out from anywhere how to actually use these two functions, can someone please explain them simply for me? I was going to make my own camera system but I saw that these functions existed and wanted to know if they'd save me time or not with my camera system.
EDIT: I looked at the example and it made sense to me, now I just need to find out why this code isn't working...

InitWindow(screenSize.x, screenSize.y, "Tower Defense Game");
SetExitKey(0);
Rectangle player = Rectangle{ 0, 0, 200, 200 };

while (!WindowShouldClose()) {
	frameTime = GetFrameTime();

	if (IsKeyDown(KEY_W)) {
		player.y -= frameTime;
	}
        else if (IsKeyDown(KEY_A)) {
                player.x -= frameTime;
        }
        else if (IsKeyDown(KEY_S)) {
                player.y += frameTime;
        }
        else if (IsKeyDown(KEY_D)) {
                player.x += frameTime;
        }
		
	camera.target = Vector2{ player.x + player.width / 2, player.y + player.height / 2 };
		
	BeginDrawing();
	ClearBackground(backgroundColor);
		
	BeginMode2D(camera);
	DrawRectangle(player.x, player.y, player.width, player.height, Color{ 255, 0, 0, 255 });
	EndMode2D();
		
	EndDrawing();
}

[TheAngriestCrusader]

Turns out you have to define offset, rotation, and zoom. I thought they had default values.