collection_select

i write the collection code.
<%= collection_select(:info, :id, @infos, :id, :user_id, options
={:prompt => "-Select a payment"}, :class =>"info") %>
which take user_id from database and show it properly..now i will want
to see it,
in controller i wrote:
@infos= params[:info][:id]
  but this will not work..error ic nil value.
what is the write code,that will help me..please povide
so taht when i choose one value from drop down.it will show the
correspoding record.