xmojmr's approach is an effective way of documenting use case scenarios, and if your sequence diagrams are confusing, it's probably because they aren't adequately documented. As xmojmr says, a picture is worth a thousand words, but sometimes a few hundred words really help to explain the picture! I'd like to share a bit of background that you might find helpful.
I see the process of describing requirements as having three levels, of which use case scenarios are the third. Top level is a use case diagram, which shows how the different use cases in a system and the stakeholders using the system interact. Next level is the details of each of those use cases. I use a "use case narrative" for this. Third level is each individual path ("use case scenario") through a use case.
There is a lot of confusion out there between levels two and three. This is partly because to some extent they run together, for example it's reasonable to analyze related success and failure paths through a use case as one scenario rather than two. At least, I prefer to treat them as one scenario.
I prefer to use activity diagrams to document use case narratives. While you can pretty much do anything with a sequence diagram (at least the 2.0 version), IMO divergent behaviors, decision trees, and parallel behaviors are more obvious in activity diagrams than in sequence diagrams. So, one activity diagram per use case, and then one sequence diagram for each separate scenario in the use case.
In your process, it looks like sequence diagrams are not accompanied by formal use case scenario documentation. If you google "use case scenario" you will find a number of examples of such. However, keep in mind that a lot of the examples are actually documenting what I'm calling "narratives".
I'm using the terminology in Tom Pender's The UML Bible (Wiley Publishing, 2003). Another great book is Alistair Cockburn's Writing Effective Use Cases: here is a good-sized sample.