I would like to know about the emails i receive requesting me to review an article of some journals ...is it a paid request or i will review it for free ?
Reviewers are almost never paid for reviews and done for free!
It is good to review for journals that are accredited and listed in one or more of the well know indices (IBSS, ISI, Scopus, etc). - a list is attached.
Also ensure that the journals are not predatory in nature - refer to Beall's list via https://beallslist.net/ in this regard.
You can also receive recognition for your reviews on a platform such Publons - https://publons.com/about/home/.
Peer review is almost always an honorary task which helps other researchers get the most out of their work. This is a very important concept in academic research. It will also help you develop your analytical skills.