Topic: Reading 'query values' from View into the "find_by_sql" method?

I'm turning many circles here trying to learn a fundamental lessonn of how the Rails community provides 'end user' query capabilities. For the last few days, I've been hit with the hard reality is that they DON'T and Web 3.0 is far off. I've been told acts_as_ferret is the way to go, but this is actually FAR off point as it focuses on building massive index engines that are perpetually maintained.
Thus, I've decided to try to create my own 'query strategy' by reading the users' query request and passing it to a Model.find(:all, :conditions => {:fieldname => @fieldname }) or fill in a Model.find_by_sql(I have no idea what goes here?).
If there were a set number of fields and the user HAD to fill in them all, then I can imagine how the first example would be written, but if the user wants to randomly decide what parameters are pertinent, what do I do with the empty ones?
Could someone write a simple example of taking ONLY one of two available field parameters on a calling form and pass them to either of the find approaches?
I'm trying to observe a RESTful approach. Is this logic supposed to be in it's own controller? and what actions am I performing here (in cadence with the 7 RESTful ones)?
I am willing to pay or share whatever I come up with here.
Thank you,
David