My question is that what is the explanation of "Taqleed", and who should do Taqleed and who is free from it? And up to what extent one should do Talqeed and which Islamic practices come under Talqeed and which don't?
Taqleed means imitation. Most Muslims fall under Taqleed since they "imitate"/follow a specific school of thought. (Maliki, Hanbali, Hanafi, Shafi'i)
The average Muslim can free himself from a specific school if he/she is interested in a specific topic and looks up all the positions held by all schools of thought, and then chooses/follows the position/interpretation he/she believes to be the strongest.
You can't really escape Taqleed since any position you choose is practically choosing a scholars position.
The only ones who can separate themselves from Taqleed are scholars and students of knowledge. These individuals are aware of the due Islamic Academic research needed to derive a ruling/position on their own. This is akin to writing a PhD paper. You have to be an expert in that one topic and aware of the proper process of research and the derivation of evidence. This is called "Ijtihad". (Academic Effort) - Mind you, it can take up years of research to derive a single position. Laymen do not have time nor the academic tools to embark on such a journey.
And Allah (SWT) knows best