Backlinks are links from other websites that point back to a website. Backlinks are important for SEO because some search engines, especially Google, will give more credit to websites that have a good number of quality backlinks, and consider those websites more relevant than others in their results pages for a search query.
No. Getting backlinks from spammy websites or unrelated-to-your-business websites will not help you but most probably will harm your rankings.
The main categories are two (2)
* Do-follow backlinks
* No-Follow backlinks