A large part of deciphering a puzzle is figuring out what code was used to cipher the message. To identify a cipher, try Googling any information about the cipher you have (e.g. what it looks like, how it is used, or any keywords).

Useful Ciphering and Decoding Resources:

https://www.dcode.fr/en

https://www.quinapalus.com/qat.html

https://wordsmith.org/anagram/

https://nutrimatic.org/

http://puzzledpint.com/resources/

This is by no means an exhaustive list. Puzzle designers use hundreds of different ciphers and often try to find original ways to cipher messages.