...means "I am Reina Tanaka". Wierd huh? That's because the Japanese say their surnames first before their given name...
Anyways "Desu" is probably one of the most common and overused Japanese word in the world. It's is used just like the English word "be". This word, however, is usually found at the end of the sentence. It also does not change to past or future tense unlike the English word "be", which could alternate to "was", "is" and "will be". If you know Filipino, it's Tagalog equivalent would be "po". It is pronounced like "dess", the letter "u" is silently pronounced by giving off a small exhale at the end. It could also be shortened to "de", but such form is rather informal.