The High Definition Render Pipeline (HDRP) includes its own purpose-built implementation for post-processing. This is built into HDRP, so you don't need to install any other package.
Post-processing effects in HDRP use the Volume framework. You add post-processing effects to your Camera in the same way you add any other Volume Override.
Note: HDRP already enables some post-processing effects in the HDRP Global Settings, go to Section Volume Profiles.
Note: Some post-processing effects are enabled by default in the HDRP Global Settings.
The images below display a Scene with and without HDRP post-processing.
Without post-processing.
With post-processing.