Variables enable you to save pieces of text that you use often, so you don't have to write them out every time.
Some typical examples are:
Tone - Create a variable that encapsulates your tone, add it to any prompt.
Company Description - A variable that has the description of your company so you don't have to keep repeating the same info
Test data/User inputs - Creating variables for user inputs will allow you to dynamically test prompts, with different pieces of test data.
A few notes about variables
You can create variables on the Team Variables page, or from the prompt testing page by clicking on the variables button (below the prompt textbox on the left).
Team variables are accessible by the whole team
Prompts have the option for local variables, which are specific to a prompt
Variables can be used in both the system message and/or the prompt.
You can add variables into your prompt by:
Typing "{{"
Tapping control+space
Here is a quick video demoing how variables work: