Piecewise functions are just made up of multiple small functions that have different domains.
For example, the function below is a piecewise function:
The green part is the first half of the function and you will graph that when x is less than 1
The purple function is the second part, you graph that when x is greater than 1.
Use should deffinately use this website to help you figure it all out!
Here are some helpful videos on graphing piecewise functions.