lo is similar to "it" in English. No lo sé - I don't know it Lo siento - I'm sorry (for it, this thing). No lo quiero - I don't want it. Is it clear now or you need more examples? If yoy need any further help, feel free to ask me. Have a nice day.

There's an old expression that "words do not mean words". That expression means that words represent ideas and concepts and many times can not be directly translated. For example, you wouldn't say "lo" means "it". More correctly stated, "The word 'lo' is sometimes used when you would use 'it' in English." However, "lo" is also used in cases where "it" would not be used in English. As for your question, here's a nice article about the usage of the word "lo": https://www.realfastspanish.com/vocabulary/uses-of-lo

These do not translate so well into English. These are idiomatic sayings; 1. Lo siento ( I feel it ) = I'm sorry 2. No lo sé ( I don't know *about* it ) =I don't know

It