Heater / Ac not working properly and exhaust fumes

Check engine hoses , breathers , injector leaks , EGR valve /pipe , pollen filter .

check the clamp around the cat, and signs of soot on the heatsheild

Thanks for you answer, Please dont angry but i dont know any of them what they look like. i checked air filter, it was clean.

Hiya mate, thanks for your suggestions now i have checked the car from few mechanics and problem is exactly what you told me to check.Now exhaust is leaking from this point (circled in red) but no one knows which part is missing from these holes. Any further help please.
Many thanks

here is a picture. circled in red. something missing i dont know what?