Learn Russian: Это словарь?

In Russian, you don't need to swap words around or add helper words like "is" or "do" to ask a simple yes/no question. You just take the statement Это словарь (This is a dictionary) and add a question mark. When speaking, you make it a question entirely with your voice by raising your pitch on the key word (in this case, словарь).

Where is the word for "is" in this sentence?

Russian usually skips the verb "to be" (am, is, are) in the present tense. So, Это словарь literally means "This a dictionary." Your brain will quickly get used to automatically filling in the "is" when you translate it to English!

How do I answer this question with "yes" or "no"?

To say yes, you just say Да, это словарь (Yes, this is a dictionary). To say no, you say Нет, это не словарь (No, this is not a dictionary). Notice that for the negative answer, you use Нет for "no" at the beginning, and then place the negative word не (not) right before the word it negates.

Is the word словарь masculine or feminine? It ends in a soft sign.

It is masculine. Words ending in a soft sign (ь) are a bit tricky for beginners because they can be either masculine or feminine, meaning you usually just have to memorize their gender. However, a helpful pattern here is that almost all Russian nouns ending in -арь are masculine.