Kosh -
A couple things.
First of all keep in mind that the sole purpose of a query is to make someone want to read your script. As such, the single most important element of a query is the logline.
Believe it or not and fair or not, people actually judge your ability as a writer by your query, it is NOT simply a formality. And those who write queries as if they are just a formality almost always get rejected - unless their logline screams high concept or is exactly what a producer is looking for.
Unless you are responding to a call for submissions - "stating the purpose" is redundant. If you did not want to submit your script for consideration for production or representation, you wouldn't be writing.
As for your question. If you don't have experience, qualifications, etc. then leave that part out entirely. Pointing out that this is your first script or that you are self-taught - is not a good idea.
Remember - a good query is as much about style as content.