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".
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.