Tsukemen is a a type of ramen noodle eaten in Japan. The biggest difference from basic ramen noodle is that noodles of the tsukemen are not soaked in a soup but you have to dip into the soup.
Then, importance of ramen is more focused on soup rather than the noodle. However, the dipping soup of the tsukemen is thicker than the soup of ramen, hardly no one drinks the dipping soup. On the other hand, quantity of the noodle is much more than the quantity of the ramen noodle, sometimes the portion is double.
Dipping the noodle into a soup or sauce is a Japanese way to enjoy the noodles. Other types of noodles, udon and soba are also eaten as dipping into sauces but the difference between tsukemen and soba/udon is that udon/soba's noodles and sauces are cold but tsukemen is lukewarm.
Tsukemen is not offered at all ramen diners and therefore if you want to try it, better to research before entering the diner.