Seattle
City Of Seattle
proper noun
The name of the city (シアトル／しあとる) with a 市 attached to it means it is "the city of ____." You can do this with any city (try it out on your hometown!). So this word means Seattle, or more specifically City of Seattle.
This word uses on'yomi reading, which you learned with the kanji.
今はシアトル市にすんでいます。
I live in Seattle now.
わたしのお母さんは、シアトル市でそだちました。
My mother grew up in Seattle.
シアトル市にはマリナーズというベースボールチームがある。
Seattle has a baseball team called the Mariners.