I was watching One Piece and come up with some words like Haki and Conquerors Haki, but I failed to understand what is the difference between them, and if there are other kinds of Haki, what are they?
The Conqueror's Haki is a subcategory of Haki.
Broadly speaking, there are two types of Haki available to everyone, given the proper training; however, there is a third type that only a certain group of "chosen ones" are said to possess.
Kenbunshoku Haki, also known as Mantra on Skypiea, is a form of Haki that allows the user to sense the presence of others, even if they are concealed from view or too far to see naturally.
Busoshoku Haki is a form of Haki that allows the user to use their spirit to create, in essence, an invisible armor around themselves. Notably, this form of Haki can be used to injure Logia Devil Fruit users.
Haoshoku Haki is a rare form of Haki that cannot be attained through training. Only one in several million people have this ability. This type of Haki allows the user to exert their willpower over others.