今天和明天
Today and tomorrow

今天我去学校。明天我去学校。现在我去学校。

Look at 去 in all three sentences: it is the same single syllable every time. English would have made you choose between 'go', 'went' and 'will go'; Chinese asks you for nothing. The verb has no time built into it at all — the time word carries the whole load, and if you change it the sentence moves in time without the verb noticing. This is not a shortcut or a simplification: it is how the language works everywhere, for every verb.

今天、明天、天

天 tiān is 'day' (and also 'sky'). 今天 is 'this day', today; 明天 is 'bright day', tomorrow, because the sun comes up on it. Both are time words, so both go in front of the verb, exactly like 早上 and 晚上 in the last lesson: 今天我吃饭 or 我今天吃饭, never 我吃饭今天. 现在 xiànzài, 'now', follows the same rule.

今天下午，明天中午

Time words stack from the big unit to the small one, and Chinese keeps that order without exception: 今天下午 is 'today, afternoon' — this afternoon. 明天中午 is tomorrow at noon. Never 下午今天. 下午 itself is built the same way: 午 is the noon point you met in 中午, and 下 means 'below', so the afternoon is the part of the day that falls below noon.

今天我……，明天我……。

Say one sentence about today and the same sentence about tomorrow, changing nothing but the first word: 今天我去学校。明天我去学校。 Hear how the verb refuses to move. Then build 今天下午 and 明天中午 into two more sentences, and finish with 现在我……, saying what you are doing at this very moment.