Es un oso could be translated as "You are a bear" or "It is a bear" ---> "usted es un oso" or "él es un oso". It is unreal that we could be talking to a bear, but we could be saying that somebody is like a bear!!!! strong, big, fat... In Spanish as in Portuguese, it is common this approach: "es un oso"/"é um urso" for saying "you are like a bear"
Except for the question mark, they look the same when written, but the pronunciation for a question would be different - it would be asked with a rising intonation. Spanish puts an upsidedown question mark at the beginning to clue you ahead of time to read it as an question (since the wording for a question or a statement can be the same).
In English you really dont say it is,you say it's,which is a combined word made up of it and is.Does this apply to Spanish?Wait,dont answer that.Run.IT'S A FLIPPING BEAR !!!!!AND WE ARE SITTING IN FRONTT OF A MOBILE DEVICE!RUN FOREST,RUN!AND EVERBODY ELSE!!!IF YOU CANT RUN GET A GUN OR SOMETHING BUT OTHER THAN THAT JUST KEEP RUNNING!!!!!!!!!!!!!!!!!!!