还

还 (hái) is a high-frequency adverb that does several jobs English splits across different words. (1) 'Still' — an action or state continuing: 我还在工作 ('I'm still working'), 他还没来 ('he hasn't come yet'). (2) 'Also / in addition' adding another item: 我要茶，还要一杯水 ('I want tea, and also a glass of water'). (3) 'Even more' in comparisons: 今天比昨天还热 ('today is even hotter than yesterday'). (4) Softening filler in spoken evaluation: 还可以 ('it's okay / not bad'), 还行 ('alright'). The same character also reads huán and means 'to return (something)' — 还钱 (return money), 还书 (return a book) — but that's a different word that just shares a glyph. For HSK 2, hái is what you need: it almost always sits before the verb, and 还没 (hái méi, 'still haven't / not yet') is one of the most useful patterns in conversational Mandarin.

Note: Toneless 还 doesn't exist — but the same character has a second reading huán meaning 'to return' (as in 还书 huán shū, return a book). Beginners almost always need hái.

Memory hook: Hear hái as 'hi, still here!' — the action hasn't stopped yet.