Sunspot / Solr is a great tool but I think it may be overkill for this case.
It's brilliant for fulltext searching and filtered results but requires running another database server.
One of simplest ways I've found is using the Ransack gem http://railscasts.com/episodes/370-ransack
The trick with understanding those form helpers is that there are two versions.
form_for :blah binds a form to the :blah model and expects all fields to be attributes on the model.
A search form doesn't work that way ( you don't have a 'search' attribute on a model )
All the form helpers not using a model end with the word 'tag' e.g. form_tag, checkbox_tag etc. and will just create form tags and pass through values without expecting anything to do with a model.
I'd suggest watching one of the earliest railscasts on a simple search form http://railscasts.com/episodes/37-simple-search-form and then using ransack for the more advanced one.