From main menu go to Window -> Show View -> Other… and select Task List and Task Repository.
Right Click o Task Repository view and select Add Task Repository on context menu.
Select Redmine as shown in the following picture.
Insert your Redmine Server URL and give a Label to the repository.
To make authentication working (thanks again to Alfonso which suggested the solution https://github.com/ljader/redmine-mylyn-plugin/issues/27) username e password are not needed you need to find your API key from your Redmine installation.
In your Redmine, to get the API key, go to My Account and and click on Show link on the right:
Copy your API key
In Add Task Repository configuration window selected Enable on API-Key field paste your key.
Click on Validate Settigs button and click on Finish button.
Eclipse will ask if you want to add a query on the Task List for the repository. Click on Yes button.
Select << Create a new query>> and click Next > button.
For example you can create a query to view all tickets assigned to yourself.
In the following picture you can see that I have created two query (in the picture I removed (thank you GIMP) the title of the tickets after the ticket number)
In the Taks List view you can create a new ticket using the context menu with right click.
all the project field will be shown as in your Redmine installation.
That’s all Folk.