I am now woking on SEO for my niche site. Some expert suggests me that I need to create mostly Dofollow backlink for ranking my site in Google. But I can't find which site can give Dofollow backlinks. Recently I increasing backlink by commenting different blogs related to my niche. But I found that all the links are Nofollow. I am afraid about this situation so need help from SEO experts.
1. How can I understand which type of link will give to my site before commenting a site?
2. What is the negative effect of Nofollow backlinks?
3. Should I remove those Nofollow links from my site?
Please, experts, are requested to solve my recent problems. I will be grateful.