Concerning your first question, see these related discussions:

https://www.researchgate.net/post/What_is_the_motivation_for_reviewing/1

https://www.researchgate.net/post/What_are_the_reasons_or_advantages_that_make_a_scientific_researcher_accept_to_be_a_reviewer_in_a_scientific_journal/1

https://www.researchgate.net/post/What_is_the_benefit_of_being_a_peer-reviewer_of_scopus_journal/1

Concerning your second question, see:

https://www.researchgate.net/post/Start_being_a_peer_reviewer/1

https://www.researchgate.net/post/How_to_be_a_peer-reviewer/1

https://www.researchgate.net/post/Does_becoming_a_reviewer_for_a_refereed_journal_require_applying_for_the_position_Or_the_journal_can_identify_a_scientist_based_on_publications/1

Certainly. Peer-reviewing allows you to expose yourself to more papers in a capacity to evaluate them, and also get to build your portfolio in research. Journals usually post these openings on their websites in the announcements/news.

The reviewing brings multiple benefits to the academicians. It gives you the visibility amongst your peers. Your CV will definitely be enriched with this kind of experience. Most importantly, you will also get to know what mistakes you should not commit while writing your own papers, since you know the process now and what type of questions or mistakes you should avoid. Along with this, some journals give you points which you can redeem while paying APC for publishing in those journals. Ther are multiple others, which you will get to know once you become the reviewer. With regards to the second question, You can go to the webpage of reputed journals and see if they have call for reviewer or editors and apply. They will consider you if you have a good research profile and your research experience will be useful analysing the papers in a productive manner. Because while doing review, you should not only select or straight way reject papers, you need to give productive suggestions also so that the researcher can improve upon his/her writing and researching skills for making revisions and writing new ones. I hope I have answered your question.