If you have difficulty with a manager or a coworker, it is generally best to request a meeting with the other person and discuss the problem in an unemotional way. Be diplomatic. The objective is to reach a solution, not to get embroiled in an argument that will only make matters worse.
"Difficulty" can be broadly defined as any work dispute, personality conflict, or other problem that makes it unpleasant to interact with another person. A manager or coworker is not breaking any law by exhibiting hostility, shouting, or even verbally abusing an employee, even though this behavior may be inappropriate. However, the verbal abuse could constitute illegal behavior if it involves a racial or religious slur or sexual harassment of any kind. Any physical abuse could be illegal.
Document any questionable or disturbing interaction with a boss or coworker by writing down the date, the nature of the interaction, and if possible, the specific words the person said. Note the names of any witness present during the incident. Next, find out what your employer's policy is on voicing complaints about bosses or coworkers. If the company has a grievance process, follow the steps for making a formal complaint. If there is no grievance process, seek advice from the human resources department.
If you are convinced that the difficulty or disagreement involves something illegal, such as discrimination on the grounds of race, gender, or age, it is likely you will need to seek legal advice. To have a legitimate case, you'll need documentation in the form of notes, e-mails, or other written documents, along with statements from any witness.