Core difference
和 (hé) is fundamentally a conjunction — a "plus sign" between items of the same category: 我和他 (him and me), 茶和咖啡 (tea and coffee). 跟 (gēn) is fundamentally a preposition meaning "with" that introduces a partner or counterpart in an action: 我跟他说话 (I am talking with him). The confusion arises because spoken northern Mandarin (especially Beijing) also uses 跟 as a conjunction, making 跟 feel interchangeable with 和 in casual speech. In written Chinese and in Taiwan, the distinction holds firm.
When to use 和
Use 和 for listing nouns of the same type in any context: 苹果和香蕉 (apples and bananas), 我的哥哥和我的姐姐 (my older brother and older sister). 和 cannot usually join verbs or clauses — "I eat and drink" is NOT 我吃和喝, but 我又吃又喝 (I both eat and drink) or just 我吃东西，喝东西. 和 is strictly for noun-to-noun linking. In formal writing, 与 (yǔ) is a more literary equivalent for 和.
我喜欢苹果和香蕉。
Wǒ xǐhuān píngguǒ hé xiāngjiāo.
I like apples and bananas.
When to use 跟
Use 跟 as a preposition for "together with": 我跟朋友一起去 (I am going together with friends). 跟 introduces the partner in interaction verbs like 说 (talk), 商量 (discuss), 合作 (cooperate), 见面 (meet with): 我跟老板商量一下 (let me discuss with the boss). The English structure "A verb with B" almost always maps to "A 跟 B 动词" in Chinese. 跟 also starts subordinate clauses meaning "following / chasing after": 他跟着我 (he is following me).
我跟朋友一起去电影院。
Wǒ gēn péngyǒu yìqǐ qù diànyǐngyuàn.
I am going to the cinema with my friend.
The spoken northern overlap
In Beijing and northern Mandarin speech, 跟 doubles as a conjunction that swaps in for 和: 我跟他 (me and him), 茶跟咖啡 (tea and coffee). This sounds very natural to northern ears and is not an error. In Taiwan and in formal writing, keep 和 for conjunction use; 跟 in that slot will strike readers as regional. If you want to stay safely neutral, use 和 for listing nouns and 跟 for "with someone in an action".
The third variant: 与 (yǔ)
与 (yǔ) is the formal, written, or classical alternative to 和. You see it in book titles (《战争与和平》 War and Peace), business names (A与B公司合作), and formal documents. In everyday speech it sounds stiff. Students building written Chinese for the HSK 5-6 essay sections benefit from fluent 与 usage; conversational learners can leave it aside.
Common mistakes
Learners often say 我和他说话 (I with him talk) when they mean 我跟他说话. English "with" in action contexts almost always wants 跟, not 和. Conversely, beginners sometimes use 跟 for listing: 我买了跟... — the listing slot wants 和 in writing. Safe rule: for "X and Y" listing use 和; for "X does something with Y" use 跟. When speaking in Beijing casually, either is fine.