A haiku is an old Japanese type of poetry that has three non rhyming lines. The first being 5 syllables, the second 7, then 5 in the third. People remember how to write haikus by simply remembering the numbers 5,7,5. Haikus usually talk about spiritual and things of nature and the world. Haikus are one of the most simple types of poetry. There are not a lot of restrictions, or anything in specific that you have to talk about.
Life is what you wish,
beyond yourself you must stretch,
find your strength within.
-Roger W Hancock