Hello,
There is a simple task which I have to do, but believe me, I really don't have a clue how to do it in Mikrotik world.

I have one bridge named: bridge and vlans 1,2,3,4,5,6
I have created port with group together the bridge itself and vlans 2,3,4,5 and ether2. So the question is, how to add vlan 2,4 to ether3 as trunk port?

Thanks a lot!

Edit the entry where ether2 is tagged and add ether3 to it (click on the down-arrow beside ether2 and another field will appear where you can select ether3)

Sorry, but I'm not sure you've got the right idea.

At the moment ether3 is also part of the bridge and it is highlighted in the first line of the bridge, where vlan 2,3,4,5 is working, so I marked that port as tagged and everything is fine, but I don't want this because this configuration makes all vlans available at the ether3 (that's why I disabled ether3), so I only want vlan 2 and 4 on this port.

Let say it in different way: there is no way to use the same vlan which is tagged on ether2 on another port, because when I tried to add vlan 2,3 to ether3 as port from the same bridge, winbox returns me an error: sorry, vlan already exist. And yes, it exist on same bridge. So maybe I have to do that with two different bridges..

When you do not want the same configuration for a set of VLAN IDs you should not configure them in the same item.
Make different items for the different VLAN IDs (2, 3, 4 and 5) like you did for ID 6 and you can configure the port memberships differently.

Yes, I did it!
Many thanks for your help @pe1chl

Here is the configuration before and after.
Everything works like a charm