Hey, sorry for the late reply! No worries mate, even Indians don't really understand the caste system. I wouldn't say that I'm an expert in it either. To better explain how being of a 'lower caste" is different than simply being poor, here are some examples:

• You can be in a very good position financially but still face societal discrimination because of belonging to a "lower caste".
• You can face problems getting places to rent or even getting employment because of your caste.
• Inter-caste marriage is received very poorly by relatives. In India, joint families are still a very real thing, where saying "fuck off" to your relatives isn't always the best option that people have. In the relatively lawless North Indian States, honor killings for inter caste marriage and stuff like that is very common.

Here's another way to think about it. Imagine if US civilization (post-genocide, not pre-genocide) was 1000 years old. In these 1000 years, black Americans were slaves in everything but name. Only in the last 100 years, did they lose their slave-ish status legally. However, they still face racism till this date. One very interesting difference between racism and casteism however is that racists can recognise their hated race by looking at the color of people's skin, while casteists can recognize their hated caste by looking at people's last names. In almost all cases (except people who have changed their last names), your last name determines your caste. So... yeah. Apply most of the stuff that you know about racism in the US to the caste system to understand the problems associated with it.