Iambic Pentameter describes the particular rhythm that the words establish in a line. That rhythm is measured in small groups of syllables; these small groups of syllables are called 'feet'. The word 'iambic' describes the type of foot that is used. The word 'pentameter' indicates that a line has five of these 'feet'.
Shakespeare used a lot of Iambic Pentameter in his sonnets and plays:
"And I do love thee: therefore, go with me;
I'll give thee fairies to attend on thee,
And they shall fetch thee jewels from the deep,
And sing while thou on pressed flowers dost sleep;"
A Midsummer Night's Dream
Why don't you try writing a poem using Iambic Pentameter and enter it into one of our Poetry Competitions?