"Is the dog eating bread?"
Translation:הכלבה אוכלת לחם?
The = ה
dog (female) = כלבה (It can also be כלב if you're talking about a male dog).
is eating (female singular) = אוכלת (or אוכל if it was a male).
bread = לחם.
And to turn a sentence into a yes/no question, you can just add a question mark and intone it like you would a question in English.