For equations, move all the variable terms to the left hand side and the constant terms to the right hand side. The marginal value for the equation is the amount that the objective function would change if the right hand side were increased by 1.0. That's an intuitive description but you should keep in mind that the marginal value is only correct for differential changes in the right hand side and not the unit change that the description talks about.
For variables, the explanation is pretty much the same. The marginal value is the amount that the objective function will change if the bound (upper or lower, whichever is active) is loosened by 1.0. Again, its really only valid for differential changes and not the unit change described. It doesn't matter whether you talk about the bound or the variable. The point of loosening the bound is that the variable will move with the bound. Remember that the marginal value is zero if the variable isn't pushing the bound.