There are three major noodles in Japan, soba, udon and ramen noodles. Not like pasta, these noodles have similar shapes but the ingredients are different. Soba noodle is made from buckwheat flour and sometimes wheat flour is added. Udon noodle is made from only wheat flour. Then, ramen noodle is also made from wheat flour but kansui; a type of alkaline mineral water, containing sodium carbonate and usually potassium carbonate must be added.
Also the difference is that soba and udon can be cold but ramen not. However, soba and udon must be dipped into a cold sauce based on soy sauce but ramen can be dipped into a warm sauce.
Especially in Czech Republic, people think udon, soba or ramen noodles in the warm soup are SOUP with noodles, which Japanese never consider. Therefore please do not say "Can I have soup with udon?" in Japan!