What are mirror twins?

How are twins formed? I am the first in my family to have twins. My children are not yet born. How would I know if they are identical twins or not? Can I know before they are born? Are identical twins also known as mirror twins? What is with mirror twins? How would I ever be able to judge who is who? Can parents confuse their twins, or do they just know. What would be different with the mirror twins? I have heard that twins can hear each other’s thoughts. They can talk through telepathy is that true? If one get hurt, does the other one feel it?