I have a sonoff zigbee 3.0 dongle and the plug-in I use is the standard that is found when I start from scratch, sorry, sitting at work and writing this, so can’t remember the name.
But I see people talking about mqtt and zigbee2mqtt. What are those? Should I use one of these to connect to my IKEA blinds instead of the standard that was found?
Sorry for my n00b questions. 
ZHA is the standard Zigbee stack:
Plug the Sonoff 3.0 in, and it should be auto-configured (on HASSOS at least).
Before you plug it in though, watch this…
See this topic:
The official “Zigbee Home Automation” (ZHA) integration is the Zigbee gateway solution that is natively built into Home Assistant and is what is official supported by the Home Assistant founders + Nabu Casa (and really the Zigbee gateway solution that this specific forum is about other than Zigbee devices/hardware products that can possibly be used with this official ZHA integration).
Zigbee2MQTT (a.k.a. Z2M) is an alternative third-party Zigbee gateway that is available as a stand-alone application well as an add-on for Home Assistant. Zigbee2MQTT communicates via the MQTT protocol which makes it more flexible, however, you can not control everything from within Home Assistant’s own user interface and you need to go to Zigbee2MQTT GiHub repository for discussions and reporting issues.
Those two Zigbee gateway solutions have many different pros and cons. Since that official ZHA integration is embedded into Home Assistant’s core it is easy to get started with and feels more like it is a native part of the Home Assistant platform out-of-the-box, and the statistics in Home Assistant Analytics does today show quite a high percentage of installations of the “Zigbee Home Automation” (ZHA) integration, which is not surprising since this is the integration that is recommended for the official Home Assistant Skyconnect dongle/adapter and Home Assistant Yellow appliance’s Zigbee radios. And with Zigbee2MQTT using MQTT which is a widely adopted standard, it makes that compatible with most other home automation ecosystems but Zigbee device management needs to at least partially be handled outside of Home Assistant’s UI, still, together with the fact that it uses MQTT and can be said to be more mature as a complete gateway solution due to it being around for a longer time makes Zigbee2MQTT quite popular among many open-source developers from other projects too and thus it usually gets full support for newer Zigbee devices and unusual features quicker than what ZHA does (though because of how the zigpy library that ZHA’s depends on is designed it will the other hand get initial support even quicker if a device is only using standard Zigbee features and functions since they will in theory then just work without any code being modified).
ZHA docs explain most need to know about how Zigbee works (like how it depends on mesh network):
Especially read and try to understand all in these sections from the ZHA integrations documentation:
Also highly recommend reading all the tips my original post in this thread:
If nothing else then avoiding interference remember network mesh is the key and simply adding more and more Zigbee Router devices to your network will make it more and more robust.
PS: There are no “plug-ins” in Home Assistant. There are instead; integrations, add-ons, scripts, and automations, including Blueprints which are pre-built automations, (as well as automation templating)