Question

I realized I’ve been switching between them with no understanding as to why, and am finding it hard to search for.

Answer 1

' ' and " " are the same thing; they are used to define string literals.

Things without quotes can be an identifier, keyword, non-string literal, property name or a number (may have missed one).

Examples:

"hello world"        literal (string)
'hello world'        literal (string) with same contents
document             identifier (object)
{ a: 1 }             property name
if                   keyword (start conditional statement)
3.4                  literal (number)
/abc/                literal (regex object)

String literals that are enclosed in single quotes don’t need escaped double quotes and visa versa, e.g.:

'<a href="">click me</a>'    HTML containing double quotes
"It's going to rain"         String containing single quote