Learn Russian: Где словарь? Он не здесь. - Where is the dictionary? It is not here.

Nouns ending in a soft sign (ь) can be either masculine or feminine, so you usually just have to memorize their gender. A big clue in this sentence is the second half: we use он (he/it) to refer back to словарь, which tells us it is a masculine noun.

Why do we use он to mean "it"? Doesn't он mean "he"?

Russian doesn't have a single universal word for "it". Instead, you use the pronoun that matches the noun's grammatical gender. Because словарь is a masculine noun, we use the masculine pronoun он, even though a dictionary is an inanimate object.

Where is the word for "is" in both of these sentences?

Russian drops the verb "to be" in the present tense. To ask "Where is the dictionary?", you literally just say "Where dictionary?" (Где словарь). The same rule applies to the second sentence, which is literally just "It not here" (Он не здесь).

I see a soft sign (ь) at the end of both словарь and здесь. What does it actually do?

The soft sign doesn't make a sound of its own. Instead, it tells you to pronounce the consonant right before it softly. For the р in словарь and the с in здесь, it sounds like you are adding a very faint, quick "y" sound right at the end of the word.