il, le, or ça?
I know that « il » doesn't necessarily refer to a person and can act as a placeholder, e.g. « il mange une araignée » is translated as "it eats a spider". Duo has also given me the sentence « il le connaît » meaning "he knows it", so « le » can act as a placeholder too.
Also, google translates « ça » as "it".
So my question is; how do we know when to use « il », « le », and « ça » ?
If a noun directly follows a verb, then you would use a direct object pronoun. Direct object pronouns include le, la, l', me, te, nous, vous, les.
Il le connaît = He knows it/him.
Il les connaît = He knows them.
The pattern continues.
I don't really know about the ça example. I do know that "il" can be used as "he" or "it", but I don't know the rules in which "c'est" would be more preferred than "il est".
When followed by un homme, une femme etc, always use c'est, never Il est, elle est. In other words always say c'est une..., c'est un...
There's a skill in the French tree explaining this. Here's the link: https://www.duolingo.com/skill/fr/Gallicism%3Ail-elle-OR-c-ce/tips-and-notes
Someone else on Duo once led me to this link: https://www.frenchtoday.com/blog/french-grammar/cest-versus-il-elle-est
Essentially, one uses « c'est » when a noun follows, and « il est » when an adjective follows. There are exceptions, of course, which the article discusses in greater detail.