Understanding MVC for Rails 4 with image upload form - ruby-on-rails

Question

I am learning rails and I am trying to understand how the MVC model works with rails 4. I am practicing this by creating a form that will allow the user to upload an image with a name to the database. I am using CarrierWave to handle image storage in the database. This is what I have so far. As I am new to Rails 4, I'm not sure how all these parts connect together.
Here are my models for User and IncomePicture:
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:rememberable, :validatable
has_many :expense_pictures
has_many :income_pictures
end
class IncomePicture < ActiveRecord::Base
belongs_to :user
mount_uploader :image, ImageUploader
has_one :income_text
end
Controllers:
class UserController < ApplicationController
def create
User.create(user_params)
end
private
def user_params
# required input for params
# permit - returns a version of the params hash with ony the permitted attributes
params.require(:user).permit(:name, :email, :password, :password_confirmation)
end
end
class IncomePicturesController < ApplicationController
def create
# create IncomePicture object with params
#income_picture = IncomePicture.new(IncomePicture_params)
#
if #income_picture.save
flash[:notice] = "Income picture successfully uploaded"
redirect_to
end
private
def IncomePicture_params
params.require(:income_picture).permit(:image, :name)
end
end
view for form:
<%= form_for #income_picture, :html => { :multipart => true } do |f| %>
<p>
<%= f.label :name %>
<%= f.text_field :name %>
</p>
<p>
<%= f.file_field :image %>
</p>
<p><%= f.submit %></p>
<% end %>
I'm not sure how to create a form that will store the upload to the logged in user. Currently only the user login portion works.
I am getting this error when I try to run rails s
First argument in form cannot contain nil or be empty
on the line
--> <%= form_for #income_picture, :html => { :multipart => true } do |f| %>
<p>
<%= f.label :name %>
<%= f.text_field :name %>

Answer 1

As the error says, the first argument of form_for cannot be nil or empty which means that #income_picture, the first argument, is most probably nil. So you have to ask why this variable is nil and where should I define it.
I'm assuming that the form is under app/views/income_pictures/new.html.erb which means that the most probable action corresponding to that view is the new action under IncomePicturesController.
Add a new action in the IncomePicturesController and define #income_picture
class IncomePicturesController < ApplicationController
def new
#income_picture = IncomePicture.new
end
...
end