Shift ciphers or Caesar ciphers are a form of substitution cipher that shifts the alphabet (hence the name).

The first method is simply using a number to shift the letters. For example, if the alphabet was only the letters ABCDEFG and we used a 2-shift method to your right, the alphabet would become CDEFGAB, where plaintext "A" would be "C" in ciphertext, making the word BAD "DCF" in ciphertext.

Here's an animation to show you how it's done (this is, obviously, using the whole alphabet--the shift is three to you right):

Using that, we would encrypt, "WE ARE LOOKING FOR BLUE'S CLUES," as, "TB XOB ILLHFKD CLO YIRB'P ZIRBP."

The second method uses a keyword instead of a number. So, instead of shifting the alphabet according to number, we put the keyword down under the alphabet and then write the rest of the alphabet, excluding the letters that are already in the keyword.

For example, here we will use the word "JUPITER" as the keyword:

Using that, we could translate, "MEET ME TONIGHT," as, "GTTQ GT QKHBRAQ."