Rails Migrations can be used to alter the database.Migration allows ruby to define the changes in database schema in a consistent and easy way.
So If one deleloper make some changes in database schema, the other developers just need to update, and run "rake db:migrate".
Using Migration we can create a new table, delete a table , add a new column in existing table and many more.
Migration support all the basic data types with valid options

Lets create a migration using the generate script.

rails generate migration products

It will create a file in db/migrate directory. The name of the file will be in the form of YYYYMMDDHHMMSS_create_products.rb

Open the file and you will get something like this:

class CreateProducts < ActiveRecord::Migration
 def change
  end
end

You can alter this file

class CreateProducts < ActiveRecord::Migration
  def change
    create_table :products do |t|
      t.string :name
      t.text :description
 
      t.timestamps
    end
  end
end

Finally run the migration

rake db:migrate

Now you can see there is a table in your daabase named products.