I don't how to make a cipher text at all, can you help me?
I was in your shoes about a year ago. The biggest help to me was Kahn Academy's crypto lessons (https://www.khanacademy.org/computing/computer-science/cryptography). The best thing it did for me was to define what many of the terms were without going too deep into the math. To directly answer your question, the most basic cipher is letter substitution: A = D, B = E... So to create the cipher, add three letters to each plaintext letter. To get the plaintext back, subtract the same number from each letter. Tada! You have a cipher text!