In Russian, what does the рас in front of рассказать

In Russian, what does the рас in front of рассказать mean? How is it different to just saying сказать?

My wife says that сказать means “to say” whereas рассказать means “to tell” as in to tell a story.

Prefixes such as ‘рас’ are extremely important in Russian. If you can understand the foundations of the various prefixes and become familiar with their uses, this will open up a whole world for you much more quickly than learning words one by one/by rote. You can find insights into this subject online, e.g. here: Russian Prefixes, Derivational Morphology – therussianblog

Although in many situations both words can be used interchangeably, сказать and рассказать have slightly different meanings.

сказать simply means “to say” something. For example: Скажи мне, что любишь меня! or “Мой сын сказал, что он уже взрослый.”

рассказать usually means to go more into the details while saying something, or “to narrate”. For example: “Он рассказал нам о своих планах на будущее.” or “Мы всегда рассказываем детям сказки.”

There’s also a short book, ‘Russian Root List’ by Charles E. Gribble, which includes prefixes and suffixes. I think they introduced it in 3rd or 4th year Russian. It really does open another world.

I would say that the general meaning of “раз/рас” as a prefix in Russian is “apart”. It indicates a separation from something.
Here you have diagrams of prefix meanings for the case of motion verbs: Verbs of Motion with prefixes — LearnRussian Grammar tables
As a derived meaning, it is often used in the sense of deploying, displaying, laying out something. A good example is the verb разложить/раскладывать (http://www.wordreference.com/ruen/разложить). Think of it as the opposite of the English verb “put away”. You put something away when you want it to be out of the way, safely kept. You “put it apart” (to translate the Russian verb literally) when you want to deploy it, set it up so it can serve its function.

Сказать = tell, say. Рас - сказать = tell something with enough detail and clearly enough that people can appreciate it, lay a story out

I love this explanation! Good verbs of motion table as well. Thanks!

I’m glad if it helped

I liked it. I liked the way you were clear, accurate and brief, while giving enough meaningful and memorable detail.

Thank you for your explanation. Helped a lot.