ohh, very nice
ok, so I can take a shelly relay :
Shelly 1 Switch Module Configuration for Tasmota (blakadder.com)
and flash with Tasmota
One more question - for simplicity, is there any chance to open tasmota configuration webpage as special window directly in openhab UI?
Well, sure, but if you’re getting a Shelly then you may find that the Shelly UI is good enough - you might not need to flash with Tasmota. Have you researched the Shelly software?
Don’t know. I presume there is a widget which allows a hyperlink to whatever webpage you like, but I’ve never tried this so someone else will have to confirm.
I found this :
https://community.openhab.org/t/tasmohab-integrate-your-tasmota-devices-easily/124027/3
but not sure how to implement
You will gain an enormous flexibility by adding Tasmota controlled devices to your setup. The flexibility will be leveraged by the additional knowledge and techniques learned in the process of introducing Tasmota to ESP based devices. Regarding the MQTT broker, you are already running openHAB, perhaps by itself on some computer. Instead, run openHAB in Docker along with eclipse-mosquitto in Docker as your MQTT broker using volume mapping for persistent data. Run Portainer as a third Docker container to be able to manage your Docker setup via any web browser.
Tasmota is quite mature in regard to exactly what devices and control features you want in addition of course to the timer scheduling. You may find much of your automatic control will be occurring at the Tasmota device level instead of at the openHAB level. OpenHAB may wind up being used primarily for an integration monitor.
It used to be that just about all retail smartplugs used an ESP8266 mcu module, which is easily re-flashed with Tasmota. Nowadays the same brand smartplugs use a different mcu module that cannot be re-flashed with Tasmota, but often that different module can be removed and a suitable ESP8266 mcu module transplanted in its place. This is the extreme end of the previously mentioned “additional knowledge and techniques learned”. The Shelly devices are a way around this. When using ESP8266 or the ESP32 development type boards, especially the ones with a USB data connection, you have the foundation for any wi-fi based Tasmota sensor and control device less a power supply and the sensor and controlled devices. As already mentioned, Tasmota is quite mature. I doubt there is anything you would like to do, even the most obscure need, that has not been already addressed in some way with Tasmota.
I’m running a openHAB on the odroid n2+ and DietPi. I’m not so experienced, so I’m happy that’s working 
and not sure which steps to do to get MQTT working (and also not sure that I need it). For me it looks too complicated and I have one important request : Be able run openHAB only with local network.
As an MQTT broker is usually installed within the same network (often the same device) as openHAB, it will be local.
Fair enough. What other option will you go ahead with?
At this moment I have only shelly relay and shelly motion - for this Mqtt isn’t necessary. Other my devices uses a modbus and serial port, so also not mqtt. But yes, maybe in the future I will need. And yes, a lot of devices works only with mqtt so I will need in the future. In general I have nothing against mqtt.
ok, on the end I decided to try install a mqqt
I used this guide
Mqqt is online. Now I must search for device for tests. Maybe I will flash some arduino board with Tasmota or Shelly 1.