Learn Russian: Март — хороший месяц.

In Russian, the present tense of the verb "to be" (am, is, are) is almost always skipped. When a sentence simply links one noun to another noun—like linking Март (March) to месяц (month)—a long dash is often used in writing to take the place of "is."

How do I know what gender to use for the adjective хороший here?

Adjectives must match the gender of the noun they describe. Here, the adjective describes месяц (month). Because месяц ends in a consonant (ц), it is a masculine noun, so the adjective must also be in its masculine form (хороший).

Why does the adjective хороший (good) end in -ий instead of the standard masculine -ый?

Usually, masculine adjectives end in -ый (like новый, meaning new). However, Russian has a strict spelling rule: you can never write the letter ы after certain consonants, including ш. You must use и instead. Because the stem of the word ends in ш, it is spelled хороший.

Why doesn't the letter я in месяц sound like a clear "ya"?

In Russian, vowels change their sound when they don't have the stress (the spoken emphasis) of the word. The stress in месяц is on the first syllable (ме). Because the я is unstressed, it "reduces" to a shorter, weaker sound, sounding closer to a quick "ih" or "ee" rather than a full "ya".