4 tone marks above the words in pinying

hello I am just starting to learn Chinese, can anyone help me with what difference the 4 tone marks make to the letter below them when writing pinying thanks Will

The marks above the vowel indicates which of the four tones to use (high, rising, low, falling). Rocket Chinese has detailed explanations in their lessons: http://members.rocketlanguages.com/lessons/283 http://members.rocketlanguages.com/lessons/285 They also have a Survival Kit lesson specifically devoted to tones: http://members.rocketlanguages.com/lessons/997