No-follow is an HTML attribute value used to instruct search engines bots that a hyperlink should not influence the link target’s ranking in the search engine’s index. It is intended to reduce the effectiveness of certain types of search engine spam, thereby improving the quality of search engine results and preventing spamdexing from occurring in the first place.
Do-follow links allow google (all search engines) to follow them and reach our website. Giving us link juice and a backlink. If a webmaster is linking back to you with this link both Search Engine and Humans will be able to follow you. The best way to give someone do-follow love is allowing keyword in the anchor text.