Fixed braces are made of an 'arch wire', which is fixed to the teeth by special holding clips (made of metal or clear plastic) called 'orthodontic brackets'.
The arch wire is bendy, and is specially shaped to fit snugly against the teeth to move them in the right direction.
Brackets are fitted to the teeth with a special 'cement', so that they don't fall off. They can be made of metal or plastic, and have grooves in them for the arch wire to clip into. Elastic bands are usually used to secure the wire to the brackets.
Arch wire and brackets may need to be changed from time to time to keep up with the teeth as they move.
It is very important to keep teeth clean when you have any type of brace, especially a fixed one. Teeth can decay around where the brackets are attached if you are not careful, and your dentist can show you how to clean your teeth properly to stop this happening.