Running multiple Wolfram Language kernels allows you to execute different commands at the same time. This enables you to, for example, continue using the Mathematica front end interactively while simultaneously and separately executing long evaluations. To use multiple Wolfram Language kernels, configure a new kernel and set up a new notebook to use it. The process is similar to connecting to a remote kernel, except that the new kernel is local instead of remote.

1. Start Mathematica.
2. Navigate to the menu item Evaluation ► Kernel Configuration Options.
   
   The Kernel Configurations dialog appears.
   
3. To add a new kernel and configure it, click Add. On macOS, click the “+” symbol at the bottom left. The Kernel Properties dialog appears.
   
4. Enter an appropriate name for your kernel, such as “Second Local Kernel”.
5. Under Basic Options, verify that “Launch on” is set to “Local Machine”.
6. Click OK to confirm the kernel settings.
7. Open up a new Wolfram Notebook.
8. Navigate to the menu item Evaluation ► Notebook’s Kernel and click the name of the newly configured kernel.
   

This notebook now uses the new kernel. Any evaluations in this notebook are performed completely independently of and concurrently with evaluations in other notebooks.