House elf’s are creatures the are very loyal to its family that they serve. You can usually find house elf’s serving old wizard families, like the malfoy family or the black family. House elf’s have to do whatever they are told to do, or they’ll have to punish themselves. House of scan be freed, if their master presents them with clothes.

Many house elf’s are treated very well, and they love working. But some house elf’s are treated very bad, and they don’t want anything else than to be freed. At many schools, there are house elf’s who clean the school at nights, and cook the food and do much more things.

House elf’s have their own kind of magic, and can for example apparate to places where witches or wizards can’t. House elf’s don’t need to use wands for their magic, they can do it with bare hands.

If you treat a house elf well, it’ll be happy to protect you and help you. Even though it’s a free elf it’ll pretty much help you and be loyal to you if you treat it well.

Some well known free elf’s are Dobby and Winky.
Dobby served the malfoys, until Harry Potter tricked Lucius to give Dobby a piece of clothing. Dobby got very happy after being freed, since he was mistreated. He then got a PAID job at Hogwarts, and even had holidays.
Winky served Barty Crouch, but was freed when she failed at her work. She got depressed and was ashamed of being a free elf, so she started drinking. Then Dobby got her a job at Hogwarts and she was soon recovered and happy again.

Many house elf’s love to work, and if someone (like hermione granger) tries to free them by tricking them to take clothes, they’ll feel very insulted and resist to clean or do their work.