Yes, what do you want to know? The parameters {a,n} generate an x-y curve (suction pressure/head vs water content).
The "a" parameter controls the x-intercept (suction pressure/head axis) and the "n" parameter the slope of the soil-water characteristic curve.
In FEFLOW "a" has dimensions of [1/L] so the x-axis is head and n is dimensionless. Please correct me if I've got this backwards - I am working from memory and the reciprocal value for "a" is easy to mess up. Gravel curves are steep with low drainage thresholds (close to the water-content axis), clay curves have lower slopes and higher drainage thresholds.
Some simple rules for FITTING COEFFICIENT "a"
High "a" pushes the curve away from the the water-content axis, that is, the material has a high suction threshold before it starts to drain (clays tend to do this).
Low "a" means that water can enter at low pressure/head, that is, the material will readily admit water (sands and gravels do this).
In units [1/m] a reasonable range for most materials is 0.005 to 5 with clay at the low end (high head, low 1/head) and gravels at the high end (low head, high 1/head).
Some simple rules for the EXPONENT "n"
"n" must be > 1.0 - stick to the range approximate range 1.0 to 5.0
"n" is higher for free draining materials (I don't like values greater than 5 for numerical stability reasons but this is not a requirement)
"n" is low for materials that are hard to drain and n = 1 generates a material that does not drain under any suction!
FEFLOW has lots of alternatives for unsaturated soils - the on I'm taking about is the default model type 0 - the vanG-Mualem model. You need to specify maximum and residual saturation and the unsaturated porosity (in addition to "a" and "n").
