There are two main types of cryptograms: substitution and transposition. I'll solve one of each here. But first, some BASIC PRINCIPLES of cryptography:
When people talk about "codes" they usually really mean ciphers. A code substitutes a symbol or a codeword for an entire word or phrase; a cipher usually manipulates the individual letters. Puzzle cryptograms are always ciphers.
There are hundreds of systems for enciphering messages. However, even in serious military situations, the cryptographer usually has a good idea of which system he/she is up against. Although it is an especially interesting challenge to try to decipher a message when you don't even have that basic knowledge, we'll assume you do know which system was used in each of these samples.