Hi all , sorry for my english i dont understand a lot.
but im litttle confuse about the order pls tell me order if its correct.


Header-Catalityc- Midpipe - cat back


And more confused when here people talking about midpipie
dont know if it referring to the cat or to the other pipe plugged to the catback

 

Header-Catalytic-catback

Typically a mid-pipe refers to a catalytic converter replacement pipe. It's either a straight pipe or a "resonated mid-pipe" which means it has a small high-flow muffler to keep the noise down (cats also reduce noise).

 

^that

Header - Catalytic Converter(or midpipe) - catback

 

Depends on how "technical" you want to be.
In the pic above, the order is:
Header -> Catalytic Converter -> Middle Pipe -> Silencer/Muffler
#4 in the diagram is considered the Middle Pipe.

But we commonly combine the Middle Pipe and the Muffler together and call it a cat-back because its the piping behind the catalytic converter.
That then gives you three sections:
Header -> Catalytic Converter (or now mid-pipe since its in the middle) -> Cat-Back