On Windows, this can be done by right clicking the folder that contains your code, hover over Send to, and click Compressed (zipped) folder. This should create a .zip file with the same name as the folder in the current directory.
For Mac users, this can be done by right clicking the folder that contains your code, click Compress "Folder Name" This should create a .zip file with the same name as the folder in the current directory.
This compressed zip file is now ready to be uploaded.