How do i know if i have a cold or flu? how can i tell if i got the common cold, influenze or pneumonia?

A cold is: Usually an upper tract issue, ie clear nasal discharge and congestion. Flu is associated with more systemic symptoms including fevers and muscle aches. Pneumonia by definition involves infection of the lung itself and can be confirmed by physical exam and chest xray.

Flu worse than cold: A "cold" is an upper respiratory infection. It is usually associated with a stuffy nose and sometimes other symptoms related to that (post-nasal drip leading to cough, headache due to sinus congestion, etc.) a flu has an associated fever (increased body temperature), muscle aches, feeling bad all over. Pneumonia means you have a bacterial or viral infection in the lung.