Now means at this moment. Right now says the same moment more strongly: at this exact moment, not later.
Now and right now
now /naʊ/ — I am busy now.
right now /ˌraɪt ˈnaʊ/ — I am at the metro right now.
Try it: Lani: When are you free? Yasmin: I am free ___, but not later. Finish what Yasmin says. (now / every day / Mondays) Answer: now — Yasmin says she is free but not later, so she means this moment and no other. Free every day, or on Mondays, would not tell Lani when to come.
Try it: Wei: Can you help me after lunch? Ira: I can help you ___. After lunch I am at the library. Finish what Ira says. (on Fridays / right now / every week) Answer: right now — Wei needs help after lunch and Ira is at the library then, so the help has to happen while the two of them stand there. A Friday, or a weekly pattern, would not get Wei any help today.