The nofollow, sponsored and UGC attributes are markers that indicate a link's nature to the search engine. The sponsored marker belongs to links for which payment or other consideration was provided, including collaborations with content creators and barter arrangements. The UGC marker belongs to links arising from user-generated content, that is, in comments, discussions and reviews. Nofollow is a more general marker for a link you do not vouch for. Search engines treat these attributes as a signal, not as a command, but failing to apply them to paid links is a violation of the rules, with the risk of a penalty for both parties. In practice this means that collaborations, PR articles with guaranteed placement and affiliate links should be marked, while a naturally earned mention does not need a marker.
See also: Guest post, Backlink profile, Collaboration with an influencer.
