Learn Portuguese (Portugal): O jardim é pequeno.

The verb é comes from ser, which we use for permanent or inherent characteristics. Since the size of a garden is generally a fixed trait, we use ser. If we were describing a temporary state, like the garden being messy today, we would use está (from estar).

Why does pequeno end in an "o"?

Adjectives in Portuguese must match the gender of the noun they describe. Because jardim is a masculine noun, the adjective takes the masculine form pequeno. If we were talking about a feminine noun, like a house (casa), it would change to pequena.

How do you pronounce the "m" at the end of jardim?

In Portuguese, an "m" at the end of a word isn't pronounced by closing your lips like in English. Instead, it makes the vowel before it nasal. It sounds a bit like the "ing" in the English word "sing", but softer and more in your nose.

Do I always need the O at the beginning of the sentence?

Yes, in this case you do! Just like in English where we say "The garden", Portuguese requires the definite article (o for masculine, a for feminine) to show you are talking about a specific garden.