Bluff is a contested skill, matching your score versus the Sense Motive score of the person or creature you are trying to bluff. Bluffing is concept oriented rather than combat oriented. You try to deceive someone using your words and actions. You may add your Int or Res modifier when making a bluff check. You must describe to the GM how you intend to execute the deception. The GM may override your decision and select Int or Res at their discretion.

Impersonation is a contested skill, matching your score against the Sense Motive score of the creature you are intending to deceive. You use mannerisms, speech, and body language to pass yourself off as a type of person or a specific person, provided the target is not intimately familiar with the person you are impersonating

If you have time to disguise yourself, you gain advantage on Impersonation checks

Persuade is a contested skill, in which the character chooses Int or Res for the Persuade check, pitted against the Int and Res of the other character's Persuade. The initiating character must decide in advance which concept or idea of which they wish to persuade their target.

The primary use of Sense Motive is to counter a bluff skill, and your score is pitted against the Bluff score of the creature trying to deceive you.

Additionally, you can use it to assess the attitude of a potentially threatening creature as with Animal Handling (Sense Motive), but at disadvantage

Negotiation is a contested skill, your score versus the negotiation score of the person you are negotiating with. The winner of the check gains a contested point. A complex negotiation may include several points of negotiation. In this case, winning a single check by 5 or more gives you advantage on your next point of negotiation

Negotiate can also be used to contest a Haggle skill check, but at disadvantage

You have knowledge of all ranks in society and their inner workings. You are familiar with social protocol in a wide array of situations. Answering a question regarding societal workings or etiquette requires a check correlating to the difficulty of the question (Trivial, Easy, Moderate, Hard, Very Difficult, Near Impossible)

Training someone in proper etiquette is a DC 20 (Hard) and requires a minimum of half a day to train someone for a simple situation, a day for a more complex situation, and around a week for constant interaction in a societal group.

You have knowledge of the political world and its workings, both now, and throughout history. Answering a question regarding politics or the history of politics requires a check correlating to the difficulty of the question (Trivial, Easy, Moderate, Hard, Very Difficult, Near Impossible)