Doing things: the -요 present

Every verb in a dictionary ends in 다, and what is left when you take it off is the stem, which carries the meaning. The ending you add depends on the stem's last vowel: ㅏ and ㅗ, the 'bright' vowels, take the bright 아요, and every other vowel takes 어요. This is vowel harmony, a leftover from older Korean in which the vowels in a word tended to match, and it is why the choice feels automatic to Korean speakers. When the stem ends in a vowel, stem and ending usually merge into one syllable, so you hear 가요 and 봐요.

Only the last vowel of the stem counts, which is what catches people out with 마시다: it has an ㅏ in it, but the vowel touching the ending is ㅣ, so it takes 어요. When the stem ends in a consonant, as 먹 and 읽 do, nothing merges and the consonant simply slides onto the ending when you speak. When it ends in certain vowels the two fuse, 마시어요 into 마셔요 and 보아요 into 봐요, because Korean dislikes two bare vowels in a row. Where Hangul has no letter for the fused sound, as with 쉬어요, both syllables stay.

하다 is the most useful verb in the language because it turns nouns into verbs: 공부, 일, 운동 (undong, exercise) and 요리 (yori, cooking) all become actions by adding it. Its polite present is always 해요, so once you know the noun you know the verb. The -요 form also has no separate shape for questions or suggestions: 가요 said flat is a statement, 가요? with a rise asks, and 같이 가요 proposes. Nor does it change for I, you or she. English has to reorder its words to do what Korean does with pitch and context.