Translation:Germany is east of the Netherlands.
"ten" is a contraction of te + den. "den" is a definite article that's fallen out of use, but the contraction "ten" has stuck around in certain phrases. It's used with masculine, neuter and plural nouns. You'll also occasionally see "ter," which is a contraction of te + der. It's used with feminine nouns. "der" is yet another definite article that's fallen out of use.
As you may have guessed, definite and indefinite articles used to be inflected based on case, but it's been simplified through time. "ten" and "ter" being used in certain phrases is simply remnants of that old system. Additionally, there used to be more of a distinction between masculine and feminine, but nowadays they're usually combined as the "common gender." Try not to worry about all of this — it's not overly important to know all of this since "ten" and "ter" are usually used in relatively fixed phrases.