functional dependency

Hi,
Does anybody have some theoretical idea about functional dependencies.
I have to find non redundant covers and convert a relation to BCNF. But i am unable to understand the concept.
:confused:

Consider the following relations and the set of Function Dependencies(FDs):
SHIPMENT (ship_id, S_capacity, S_date, cargo, amount)
FDs are as follows:
Ship_id S_capacity
Ship_id, S_date cargo
Cargo, S_capacity amount
<br>
Now perform the following:
(i) Identify the key of the relation.
(ii) Find the non-redundant cover of the given FDs.
(iii) Normalize the relation into BCNF. Is the decomposition dependency preserving? Give reason for your answer.