Hey
I am new to HA.
I did a bit now and I am little lost in the concept for “non official” addons.
There is the possibility to add more Repos under “Addons”.
Addtionally there is HACS … more custom.
Now I see in HACS many inegrations … eg. Shelly which are available there but also in “normal” HA.
What is best practice to approach those diverse possibilities?
Thanks 
tom_l
2

Use the core integrations from here: Integrations - Home Assistant (no need to install anything just configure and restart). Unless:
- There is no core integration for your device or service
- The core integration does not support the features you want.
In that case use a third party integration, installed via HACS.
Same goes for Lovelace cards.

There are two official repositories of addons for Home Assistant, the core repository and the community addon repository.
You can add other repositories if there is an addon developed by someone else.