What is the difference between a dofollow and nofollow and how are they used?

Do follow link passes link juice and they definitely help you much
No follow link does not passes link juice

A no follow link is a link that does not count as a point in the page's favor, does not boost PageRank, and doesn't help a page's placement in the SERPs. No follow links get no love. Theirs is a sad and lonely life. The nofollow tag is basically a notice sign for search engines saying "don't count this."