---Initialization, this is part when you have to define all global variables and APIs to use(and hardware as well).
local term=request('term')---this will allow ya to use some terminal related functions, such as term.clear(), etc. Works with printed text only
local component=request('component')---this will allow you to use components
local gpu=component.gpu---this will allow you to use all GPU related stuff (also a reason why you had to define component)
local forecolor=0xFF0000---this is a hexadecimal numeric value of foreground color in RGB. This is Red as possible.
local backcolor=0x0000FF---this in the other hand is as blue as possible. Google 'hexadecimal colors', you will find all numbers you need.
local w,h=gpu.getResolution()---will get and store your resolution of screen in w-width and h-height

term.clear()---clears text, don't remember if there is any by default
gpu.setDepth(8)---this will set 8-bit color depth (8-bit is max, not sure if by default tho)

---now we can write some stuff
---gpu.set(x:num,y:num,text:string)
gpu.set(1,1,'Hello world!")---this will print 'Hello world' text on screen starting at 0 0 coords. See that I am not using print('text')
---.set is your way to go if you want to play with colors, it is more controllable and relayable than print()
---Text up there will be in default colors, b/w, now let's change it
gpu.setForeground(forecolor)
gpu.setBackground(backcolor)---both self explaning. Just set color of text and it's background.
gpu.set(1,2,'Hello, I am in color now!!!!')---Red text on blue background in line 2.
term.clear()---nothing happens as those typings on screen aren't terminal related, rather GPU specific things.
os.sleep(5)---sleep for 5 sec, cute, isn't it?
gpu.setBackground(0x000000)---black background
gpu.fill(1,1,w,h,' ')---this will fill rectangular area with it's top left corner at 1,1, while being w width and h high. Filled with blank black spaces.
---Screen is cleared after 5 seconds as it will fill area equal to your resolution.
os.exit()---exits program (in case you have loops this is way to go, here it isn't necessary)