The data that is stored in SharePoint lists are described by site columns. These columns can be defined at a site level and describe the data that users will enter when they add new rows in the list. Many times you will create new columns or add columns from a predefined global list of columns.
There are two different ways to add a column to a list. You can add a column from a list of existing columns or can create an entirely new column. SharePoint has a list of existing columns that are commonly used, such as address, city, date, and the like. However, if none of these commonly used columns is what you need, then you can add a new column that you create.
To add an existing column, follow these steps:
In the Settings page of a list or library, click the option to Add from existing site columns.
Once clicked, this link takes you to an Add Columns from the Site Columns page, where you can select and add columns from the already available columns. You can add any of the following columns from the existing groups to a list: Address, City, Date Created, and Status. There are many more columns, and each is listed in a category to help you find the columns quickly. The columns will be added in the order that you select them.
If none of the existing site columns matches what is needed, a custom column can be created:
On the Settings page of the list, simply click ...