Here are some ways to think about it:
* Breaking a code: If you decipher a secret message, you figure out the code or system used to write it and translate it back into normal language.
* Understanding a language: If you decipher a document written in ancient Egyptian hieroglyphics, you figure out what the symbols mean and translate them into English.
* Solving a puzzle: If you decipher a cryptic message in a crossword puzzle, you figure out the clues and fill in the correct answers.
Essentially, deciphering means making something obscure or hidden understandable.