"Tea is a drink."
Translation:Le thé est une boisson.
The "le" is because it's a general statement about tea. See rule #2 in the tips & notes:
"When an article is missing in an English sentence, it must be added to the French translation. The definite article can be used to fill this void in three situations:
1) Almost anywhere one would use "the" in English (i.e. when referring to specific things). 2) Before the subject of a sentence to state general truths about it. 3) Before the direct object of a verb of appreciation (like aimer) to express like/dislike. If any of the above is true, then use the definite article. Otherwise, use the indefinite or partitive, depending on whether or not the noun is countable.
I like wine, but I am drinking milk. — J'aime le vin, mais je bois du lait. Both articles are missing in the English version of this example. Aimer expresses fondness for wine, so le vin should be used there. However, boire is not a verb of appreciation, so the partitive du should be used on the uncountable lait.
Cats are animals. — Les chats sont des animaux. This is a general truth about cats, but #2 above can only apply to subjects, so only chats takes a definite article here. Animaux are countable, so use the plural indefinite des.
He likes to eat meat. — Il aime manger de la viande. This is a tricky example because the meat is the direct object of manger, not aimer. Thus, #3 does not apply and viande cannot take a definite article.
Also, the French definite article can be ambiguous when translating from French to English. It can often refer to both a specific noun and the general sense of a noun.
Les chats sont des animaux. — Cats are animals. / The cats are animals."