If you are a biology person, you will know that organisms are classified into groups based on similarities. These similarities can be found in cell structure, appearance, as well as ancestral lineage. All organisms on earth fall into these categories: Kingdom, Phylum, Class, Order, Family, Genus, and Species. However, these are constantly changing. For instance, about 200 years ago, organisms were plants or animals. This was not descriptive enough for some scientists, though. They decided to divide organisms into 6 kingdoms. Each kingdom has its own unique characteristics that separate it from the others.
Plantae- Multicellular organisms with a nucleus, cell wall, and chloroplasts
Animalia- Multicellular organisms with a nucleus and can move on their own
Protista- Mostly unicellular with a nucleus; multicellular have simple cell structure
Fungi- Mostly multicellular with cell wall and nucleus
Bacteria- Unicellular organisms without nuclei
Archaea- Unicellular organisms that have no nucleus, distinctive chemical makeup, and can withstand extreme conditions
Humans fall under the category of Animalia, and are related (very broadly) to dolphins, apes, and even jellyfish. This is where the other classifications come in. They separate us from dolphins, jellyfish, and apes, and group us with other humans. The full name of a human is Animalia Chordata Mammalia Primate Hominidae Homo Sapiens.
Recently, scientists have added yet another division of classification. These are called domains. A domain is the most broad classification of an organism, and there are only three domains. Any multicellular or mostly multicellular organisms are fall under Eukarya. Bacteria and Archaea have there own domains to themselves. The reasoning for this is just to show that certain organisms are related to each other, even if they seemingly have no connections. It is kind of like saying that you sister's friend's aunt's cousin's dog's neighbor's foreign pen pal is related to you. I see no actual point in this addition, unless you are into confusing biology students.
There is actually another way to classify organisms, but, it is not widely accepted. It is called Tribe. Humans belong to the Tribe Hominini. Tribes fall under family, and are more specific in an organisms DNA. It is commonly used in zoology, and not often taught to students.