Basically what they said but you can do two way talk too! For me Frigate is the way to do cameras and there is a HA addin which does take a bit of configuring but there are loads of decent docs.

Home Assistant is quite a beast but start off simple and work on. It will repay you every step of the way. The first hurdle is to get it on the internet and usable via the app. Get that sorted and you are well on your way.

Make use of dynamic DNS to register a name to IP address and Lets Encrypt to sort out a SSL cert. There are add ins for both of those.

You can also subscribe to Nabu Casa and external access and a few other things will be taken care for you. 31 day trial and https://www.nabucasa.com/pricing/