What is magnetic variation?
Magnetic variation is the error induced by the difference in location of true north and magnetic north.
The variation is expressed in east or west variation.
This means that the magnetic variation is different, in different locations.
The variation in your location, you can find out by looking on the aeronautical chart, for example Terminal Area Chart.
Then when you know the difference between true and magnetic, you can convert the true to the magnetic.
Remember East is least Subtract
West is best Add