For example if you know the F major barre chord you know that the relative minor is the d minor barre chord. The pattern is the same for G major and E minor. You are using the e configuration barre chord for the f major and you move up the neck 4 frets and use the A minor shape barre chord to create the D minor. So knowing the two different barre chord configurations using the e shape and the a minor shape you will be able to find any relative minor chord just by know then pattern.
You can also use the A shape Barre chord as the Major Chord shape and get the same results. It is even easier to remember than the previous example. Make a C major Barre Chord using the A Major Shape and move up the neck two frets and make the A minor barre chord and you have C major and its relative minor of A.
For FREE guitar software and lots lots more visit : http://www.TabGuitarLessons