What have you tried ? I would start with something like a TCP in node set to listen to a port above 1024 - eg 3333 - connected to a debug node
then set Matlab to write to that device (using 192.168.1.20 below but use your ip address) on that port - as per a write example Write and Read Data over TCP/IP Interface - MATLAB & Simulink - MathWorks United Kingdom
t = tcpclient("192.168.1.20",3333)
data = 1234;
write(t, data)
I don't have Matlab so can't test it - but assuming the manual is correct etc...
I can see a number of the previous results provided links for how to get started with MQTT. So it would be helpful if you could describe a bit more about what you have got so far and what you'd like to achieve.
As I said, i am new in this, so i need some example for beginners. What I Wish to achieve is to send data to Simulink via Mqtt and than to make some data analyze.
to send data from Matlab using MQTT is not a Node-RED problem - maybe try the Matlab help system ? - MQTT in MATLAB - File Exchange - MATLAB Central - there seems to be a download and some docs there.