Select the column header next to where you want the new column
Right-click the selected column header
Click Insert
To add multiple columns, select the same number of existing columns first
Right-click the selection
Click Insert
Use the Home tab
Click Insert in the Cells group
Choose Insert Sheet Columns
Use the keyboard shortcut Ctrl + Shift + +
Select a cell in the column area
Press Ctrl + Shift + + and choose Entire column if prompted