Work with Patch Versions
Patch versions can only be created for Major Releases. Subscribers can receive patch upgrades just like any other package version. However, you can also distribute a patch by using push upgrades.
When you create a patch, the patchNumber on a package's Version Number increments by one. For example, suppose that you release a package with the version number 2.0. When you release a patch, the number changes to 2.0.1. This value can't be changed manually.
Patch Development Organizations
Every patch is developed in a package version, which is the organization where patch versions are developed, maintained, and uploaded. To start developing a patch, create a package version. See Create and Upload Patches in First-Generation Managed Packages. Patch development organizations are necessary to permit developers to change existing components without causing incompatibilities between existing subscriber installations.
A package version can upload an unlimited number of patches. Only one package version can exist per major release of your package. A package version for a package with a version number of 4.2 can only work on patches such as 4.2.1, 4.2.2, 4.2.3, and so on. It doesn’t work on version 4.1 or 4.3.
Integrating Patch Development
The following diagram illustrates the workflow of creating a patch and integrating any work into future versions:After version 2.0 is released, the developer creates a patch. The package version number in the package version starts at 2.0.1. As the main development organization moves towards a released version of 3.0, a second patch is created for 2.0.2. Finally, the developer merges the changes between the main development organization, and the package version, and releases the package as version 3.0.

Git source control is the best way to monitor your package versions. To learn about Git, complete the Git and GitHub Basics Trailhead module.
Version control is integrated into Visual Studio Code. See Salesforce Extensions for Visual Studio Code and Version Control in Visual Studio Code for details.