I am trying to answer in my perspective
layout in nothing but an view layer in magento 2. What you see in webpage is an layout and it can be like
1 - column, 2- coulmns-left etc..,
it will be defined in layout.xml respective to the pages you're working on.
For example :
If you're working on homepage then you must defining the layout in cms_index_index.xml likewise it varies from product page catalog_product_view.xml
and coming back to the question
1 - Column
2 - column left
2 - column right - is vise-versa of 2 - column left
3 - column
2 . How to identify layout of particular page
In magento you can inspect the page and check the body tag for layout class
It looks like
page-layout-1column or page-layout-2columns-left
and it does vary from page to page.
In magento you can verify by checking the xml file and for each page there will separate layout will be defined.
Home page - cms_index_index.xml
Cateogry Page - catalog_category_view.xml
Product Page - catalog_product_view.xml
Cart page - checkout_cart_index.xml
Checkout - checkout_index_index.xml
and for cms pages you have login to admin and find out the layout in specific to pages.
For more information visit here
Hope this information helps.