There are two types of backlinks: dofollow and nofollow. Dofollow backlinks are links that pass on "link juice" to the linked-to website, which helps that website's search engine optimization (SEO). Nofollow backlinks, on the other hand, do not pass on link juice and therefore do not help the linked-to website's SEO.
Nofollow backlinks can still be useful, though, because they can help to build relationships and drive traffic to your website. For example, if you have a blog post that is getting a lot of traction and you see that someone has left a nofollow comment on it, you can still reply to that comment and build a relationship with that person.
In general, it's best to get as many high-quality dofollow backlinks as possible. But don't discount the value of nofollow backlinks altogether.