You almost got the Chinese phrase correct but the 'you' is incorrect. It should be 你 which is pronounced as 'ni' in like 'knee' . The character you wrote was 尔 which is pronounced as 'er' and means something else other than 'you'. As for whether you know someone is saying 做 or 坐, you have to look at the context because both sound exactly the same. 做 is used when mentioning a task and 坐 is used when mentioning about seating.

坐，= sit （down） eg, 坐下sit down 请坐please sit down 我坐哪？where should i sit? 坐公交（车）/地铁 take a bus/ subway 做， = do eg 做作业do homework 做家务do housework 做任务do a mission 这件事谁做的？Who did it? anyway, the usage of "坐" is limited, usually with a meaning of "sit down" or "take a transportation" but 做 have other meaning ：）

坐means sit, e.g. sit on the stool 坐在凳子上 , 做 means do， e.g. what are you doing, 你在做什么？

There are thousands of words each having the same pronunciation, for example 作 and 座 are also pronounced zuo in the 4th tone, and 要，腰，夭，and 妖 are all pronounced yao in the 1st tone. You just have to get used to knowing the meaning by context!

just like with 他 and 她 -- from the situation