Here’s the short answer: it’s different for everyone and will probably change over the course of your studies.
For me, at first the most challenging part of learning Mandarin was pronouncing the four (actually five) tones and understanding how they work together in a sentence. I’ll never forget recording myself read passages aloud for homework in college and having a sore throat afterwards from dipping wayyyy too low for third tone. Honestly, I thought I needed to have a super exaggerated ‘down-up’ sound for each third tone and the only way I could make that happen was to force my voice to go really low.
Pro tip: no language should make you get a sore throat or lose your voice, guys. I was clearly doing something wrong.
Over time, I learned to relax my third tone and it blended much more naturally with other words. Most of the time, third tone just has to be lower than the tone that follows... listen to the recording on our Instagram post “手冲咖啡 pour-over coffee” for an example of this.
Another memorable challenge was figuring out the difference between 那 and 哪. I remember looking at an example dialogue in my textbook where someone says: “我的书在哪儿?” (wǒ de shū zài nǎr) and someone answers: “在那儿” (zài nàr). I didn’t pick up on the tone difference between nǎ 哪 and nà 那, so I thought, how can the answer to a question be the same as the word used in the question?! “Zài nǎr?” “Zài nàr.”
Of course now those confusions seem trivial to me. Now, my greatest challenge is remembering how to write Chinese characters (especially by hand!!!) I lived in China for a few years, so can understand most conversations and communicate well, but reading novels or even just writing greeting cards in Mandarin still gives me a massive headache. My handwriting also still looks like a second grader’s...
Anyway, the point is, there will always be something about the language that frustrates you. You’ll feel like it doesn’t make sense, or you’re not making any progress whatsoever. You’ll feel embarrassed when everyone else in your class seems to ‘get’ it. That’s okay! It’s totally normal. Try asking your teacher or re-read the section in your textbook again (even if you think it’s useless). I promise it will make sense one day, and you’ll look back and wonder how you ever questioned it.
That’s it for today, friends! 加油!