Integratons in HACS (or custom_components as they often are refered to) are community built integrations.
Special notes about Integrations
When you install, update or uninstall an integration in HACS, you need to restart Home Assistant.
There is 1 exception to this.
If the integration support configuration with
config_flow, you do not have to restart Home Assistant after the intallation.
You can go straight to the "Configuration" section of the UI, then to "Integrations".
You may need to clear your browser cache before you see it in the "+" list.
Note that this only applies for the installation and initial configuration of that Integration, if you update it, you still need to restart Home Asstant before it loads the new files.
Integrations download location
All the Integrations you download with HACS is stored in
custom_components/ in your Home Assistant configuration directory.