This is the 1140th most frequent Swedish word.
ja
Yes.
Here, 'ja' is used as an affirmative response, equivalent to 'yes' in English.
Ja, jag vill gå på bio ikväll.
Yes, I want to go to the cinema tonight.
In this usage, 'ja' is employed as an intensifier, translating roughly as 'indeed' to emphasize the statement.
Han hade ja en bok med sig.
He had indeed a book with him.
Here, 'ja' is used within a sentence to affirm or emphasize a part of the statement.