It can be of various kinds and it can vary from individuals to nations. For example right now Iran is the increasing target of international sanctions to put pressure on the regime to abandon its nuclear program. The United States uses various tools to exert pressure on nations and on individuals to comply with either the international law and national laws. It uses a combination of financial, military and political means to exert pressure so that it can achieve its goals. It is not only the international powers that can put pressure, even countries which do not have the military means to fight international powers. Iran for example regularly accuses arrested Americans of spying for the CIA. Pakistan puts pressure on the U.S. and NATO through blockage of routes to Afghanistan to achieve its own goals. China uses its massive currency and heavy weight to influence international matters related to Taiwan.
North Korea arrests American and accuses them of espionage and thus put pressure on the U.S. government to ease pressure on it. Parents put pressure on the kids to achieve good grades in school and teachers put pressure on students with difficult exams and if possible through detention to make the unruly students behave in a certain way. Every way you see pressure is there, you may not feel it but you are constantly under pressure every day of the week even while relaxing you are also under pressure since there is not enough time for you to relax and leave the worries of the world behind for a while. So folks the pressure tactics are can be human or it can be from nature. Either way you are pressured.