A B Minor chord contains the notes B, F#, D. It is built from the minor formula 1 - ♭3 - 5, with B as the root.
Is B minor harder than F major?
They're comparable, and most players find B minor a little more forgiving. Both need a full index barre, but B minor sits at the 2nd fret where the string tension is slightly lower than at the 1st fret, which is why it's often tackled straight after F.