Help with D3D.

This is one of my first programs with directx. The only thing thats not my code and is directly copied is things dealing with Triangles and Matrices. I dont understand what this stuff does and I need an explanation I tried msdn but it was too complicated. First i''ll display the whole thing then i''ll display the parts i need help with.

#define WIN32_LEAN_AND_MEAN
#include<d3dx8.h>
#include<d3d8.h>
#include<stdio.h>
#pragma comment(lib,"d3dx8.lib")
#pragma comment(lib,"d3d8.lib")
LRESULT CALLBACK WndProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam);
void initWindow();
void killWindow();
void initD3D();
void killD3D();
void initGame();
void killGame();
void askFullscreen();
void messageHandler();
void render();
void drawStuff();
HWND ghwnd = NULL;
HINSTANCE gInstance = NULL;
LPDIRECT3D8 pd3d;
IDirect3DDevice8 *pd3dd = NULL;
const int gheight = 480;
const int gwidth = 640;
const char gamename[] = "Cool Game 1.1";
bool fullscreen = true;
bool gameover = false;
class CVertex{
public:
	float fX,fY,fZ;
	DWORD color;
	void Create(float fx,float fy,float fz,float r,float g,float b){
		fX=fx;
		fY=fy;
		fZ=fz;
		color = D3DCOLOR_XRGB((BYTE)(r*255),(BYTE)(g*255),(BYTE)(b*255));
	}
};
const DWORD D3DFVF_CVertex = D3DFVF_XYZ|D3DFVF_DIFFUSE;
CVertex vtxTriangle[3];
int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,PSTR CmdLine,int iCmd){
	gInstance = hInstance;
	askFullscreen();
	initWindow();
	initD3D();
	initGame();
	while(!gameover){
		messageHandler();
		render();
	}
	killGame();
	killD3D();
	killWindow();
	return 0;
}
LRESULT CALLBACK WndProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam){
	switch(msg){
	case WM_DESTROY:
		gameover = true;
		PostQuitMessage(0);
		return 0;
		break;
	case WM_LBUTTONDOWN:
		gameover = true;
		PostQuitMessage(0);
		return 0;
		break;
	}
	return DefWindowProc(hwnd,msg,wParam,lParam);
}
void initWindow(){
	ULONG width,height;
	DWORD style;
	WNDCLASS wc;
	wc.cbClsExtra = 0;
	wc.cbWndExtra = 0;
	wc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
	wc.hCursor = LoadCursor(NULL,IDC_ARROW);
	wc.hIcon = LoadIcon(NULL,IDI_APPLICATION);
	wc.hInstance = gInstance;
	wc.lpfnWndProc = WndProc;
	wc.lpszClassName = "Class";
	wc.lpszMenuName = NULL;
	wc.style = CS_OWNDC;
	RegisterClass(&wc);
	if(fullscreen){
		height = GetSystemMetrics(SM_CYSCREEN);
		width = GetSystemMetrics(SM_CXSCREEN);
		style = WS_POPUP;
	}
	else{
		height = gheight;
		width = gwidth;
		style = WS_OVERLAPPED|WS_SYSMENU;
	}
	ghwnd = CreateWindow("Class",gamename,style,0,0,width,height,NULL,NULL,gInstance,NULL);
	ShowWindow(ghwnd,SW_SHOW);
	UpdateWindow(ghwnd);
	SetFocus(ghwnd);
}
void killWindow(){
	if(ghwnd){
		if(!DestroyWindow(ghwnd)){
		}
		else{
			MSG msg;
			while(PeekMessage(&msg,NULL,0,0,PM_REMOVE)){
				DispatchMessage(&msg);
			}
		}
		ghwnd = NULL;
	}
}
void initD3D(){
	D3DPRESENT_PARAMETERS d3dpp;
	D3DDISPLAYMODE displaymode;
	HRESULT hr;
	pd3d = Direct3DCreate8(D3D_SDK_VERSION);
	hr = pd3d->GetAdapterDisplayMode(D3DADAPTER_DEFAULT,&displaymode);
	ZeroMemory(&d3dpp,sizeof(d3dpp));
	d3dpp.BackBufferCount = 1;
	d3dpp.hDeviceWindow = ghwnd;
	d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
	if(fullscreen){
		d3dpp.BackBufferHeight = gheight;
		d3dpp.BackBufferWidth = gwidth;
		d3dpp.BackBufferFormat = D3DFMT_R5G6B5;
		d3dpp.Windowed = FALSE;
	}
	else{
		d3dpp.BackBufferFormat = displaymode.Format;
		d3dpp.Windowed = TRUE;
	}
	hr = pd3d->CreateDevice(D3DADAPTER_DEFAULT,D3DDEVTYPE_HAL,ghwnd,D3DCREATE_SOFTWARE_VERTEXPROCESSING,&d3dpp,&pd3dd);
	D3DXMATRIX mat;
	D3DXMatrixPerspectiveFovLH(&mat,D3DX_PI/10,gwidth/gheight,1.0,100.0);
	pd3dd->SetTransform(D3DTS_PROJECTION,&(D3DMATRIX)mat);
	D3DXMatrixIdentity(&mat);
	pd3dd->SetTransform(D3DTS_WORLD,&(D3DMATRIX)mat);
	D3DXMatrixTranslation(&mat,0,0,10.0);
	pd3dd->SetTransform(D3DTS_VIEW,&(D3DMATRIX)mat);
	vtxTriangle[0].Create(0,0,0,1,0,0);
	vtxTriangle[1].Create(0,1,0,0,1,0);
	vtxTriangle[2].Create(1,0,0,0,0,1);
	pd3dd->SetRenderState(D3DRS_CULLMODE,D3DCULL_NONE);
	pd3dd->SetRenderState(D3DRS_LIGHTING,FALSE);
}
void killD3D(){
	if(pd3d){
		pd3d->Release();
		pd3d = NULL;
	}
	if(pd3dd){
		pd3dd->Release();
		pd3dd = NULL;
	}
}
void initGame(){
}
void killGame(){
}
void render(){
	pd3dd->Clear(0,NULL,D3DCLEAR_TARGET,D3DCOLOR_XRGB(0,0,0),1.0f,0);
	if(SUCCEEDED(pd3dd->BeginScene())){
		pd3dd->SetVertexShader(D3DFVF_CVertex);
		pd3dd->DrawPrimitiveUP(D3DPT_TRIANGLELIST,1,vtxTriangle,sizeof(CVertex));
		pd3dd->EndScene();
	}
	pd3dd->Present(NULL,NULL,NULL,NULL);
}
void messageHandler(){
	MSG msg;
	if(PeekMessage(&msg,ghwnd,0,0,PM_REMOVE)){
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}
}
void askFullscreen(){
	int full;
	full = MessageBox(NULL,"FullScreen mode?",gamename,MB_YESNOCANCEL);
	switch(full){
	case IDYES:
		fullscreen = true;
		break;
	case IDNO:
		fullscreen = false;
		break;
	case IDCANCEL:
		exit(5);
		break;
	}
}

PART 1 located in the globals

const DWORD D3DFVF_CVertex = D3DFVF_XYZ|D3DFVF_DIFFUSE;
//What does this mean/do?

PART 2 in initD3D()

D3DXMATRIX mat;
	D3DXMatrixPerspectiveFovLH(&mat,D3DX_PI/10,gwidth/gheight,1.0,100.0);
	pd3dd->SetTransform(D3DTS_PROJECTION,&(D3DMATRIX)mat);
	D3DXMatrixIdentity(&mat);
	pd3dd->SetTransform(D3DTS_WORLD,&(D3DMATRIX)mat);
	D3DXMatrixTranslation(&mat,0,0,10.0);
	pd3dd->SetTransform(D3DTS_VIEW,&(D3DMATRIX)mat);
	vtxTriangle[0].Create(0,0,0,1,0,0);
	vtxTriangle[1].Create(0,1,0,0,1,0);
	vtxTriangle[2].Create(1,0,0,0,0,1);
	pd3dd->SetRenderState(D3DRS_CULLMODE,D3DCULL_NONE);
	pd3dd->SetRenderState(D3DRS_LIGHTING,FALSE);
//I dont understand D3DXMatrixPerspectiveFovLH and it''s parameters.

//I also dont understand set transform matrix identity and MatrixTranslation.

Someone please help me, I really need help. I tried msdn but there were lots of big words i didn''t understand, someone please break it down for me, it will be greatly appreciated. Thanks

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