The dofollow word comes from English which consists of the words "do" and "follow" which means "to follow". If there is a link linked in a post to another site dofollow, it means that the blog follows the linked link.
when Google Bot crawling the linked site. Google Bot will index it to its roots.
Where as the word nofollow consists of two syllables namely "no" and "follow" which means "do not follow". If the link in the post is installed nofollow, then when Google crawls, it won't be indexed at all.