first raw implementation of the form

app/controllers/supporters_controller.rb

@@ -2,4 +2,20 @@ class SupportersController < ApplicationController
   def new
     @supporter = Supporter.new
   end
+
+  def create
+    @supporter = Supporter.new supporter_form_params
+    if @supporter.save
+      redirect_to thanks_path
+    else
+      flash.now[:danger] = t 'shared.actions.failed'
+      render :new
+    end
+  end
+
+  private
+
+  def supporter_form_params
+    params.require(:supporter).permit(:first_name, :last_name, :street, :zip, :email, :support, :age_category)
+  end
 end