Learn Russian: Где мяч? - Where is the ball?

In Russian, the present tense of the verb "to be" is almost always skipped. So, Где мяч? literally translates to "Where ball?" but means "Where is the ball?".

How do we know it means "the ball" and not "a ball"?

Russian doesn't use articles like "a", "an", or "the". You figure it out from the context. Because someone is asking where it is, they are almost certainly looking for a specific ball, so "the ball" makes the most sense here.

What gender is мяч?

мяч is a masculine noun. It ends in a consonant, which is the typical ending for masculine words. Even though the letter ч always makes a soft sound, masculine nouns ending in ч do not get a soft sign at the end.

How do you pronounce the two consonants at the start of Где?

You say the г (g) and д (d) right next to each other, without any vowel between them, blending into "gd-ye". Blending consonants together like this is very common in Russian!