Packet data breakdown

[Orangeb]

Hi,
I have been going back to basics.
IF a packet header contains all the protocols - IP, TCP, UDP, HTTP, and I have been told it only needs one of these, then what happens if HTTP is selected? Because thats only application data, really? Web browser etc. Or can it work with 2, or is that the whole point of the stack idea? I have been trying to find a visual breakdown of a packet header thats not too complicated.
Maybe I just overthink stuff too much,
Thanks for reading,
Matthew.

 

[Orangeb]

I think what I mean is, the 2 models OSI and TCP/IP, show what gets sent etc, but I wanna look inside a packet. I know a packet goes in layer 3 of the OSI - but I need to know more about the packets protocols, how it is divided up, when it comes to the TCP UDP HTTP etc. What is selected with regards to that part. The explanations on the net are confusing a lot of the time.