I need to do a program that prompts the user for 3 positive numbers (or zero) and then adds them together. If the user enters a negative number, the program should reprompt them until they enter a positive number.
Besides I need to divide the program into two functions:

prompt_number - Prompts for a number, and keeps re-prompting as long as it is negative. Then, returns the number.

compute_sum - Accepts 3 numbers, adds them together and returns the sum.

main - Calls the prompt_number function 3 times, saves the return value into three different variables, then passes those 3 variables to the compute_sum function. Finally, saves the result of compute_sum into a variable and displays it.

While we are primarily here to help people with their Free Code Camp progress, we are open to people on other paths, too. Some of what you are asking is pretty trivial in the Free Code Camp context, so you might find that if you’re not getting the instruction and material you need in your current studies, the FCC curriculum will really help you get started. At a modest guess I’d say investing a 4-5 hours working through the curriculum here will really pay off. You can find the curriculum at https://www.freecodecamp.org/learn.

With your current questions, we don’t have enough context to know what you already know or don’t know, so it is impossible to guide you without just telling you the answer (which we won’t do).

It is pretty typical on here for people to share a codepen / repl.it / jsfiddle example of what they have tried so that anyone helping has more of an idea of what help is actually helpful.

Please provide some example of what you’ve tried and I’m sure you’ll get more help.