Column formulas apply to all the cells in that column, and they are a great way to automatically populate your table with information without you having to remember to adjust your formula parameters.
Let's say you want to track end dates, and each end date is 3 days after the start date. You can write a column formula for the end date column that references the start date column. First, create your start date column (doesn't matter what you name it) and then create the end date column - don't forget to choose the "date" format for both of these columns.
Now it's time to add your formula. Click any cell in your end date column and type = and the rest of your formula. You'll be able to select any of your columns and tables to use in the formula. Hit enter and your new end dates will automatically populate into your column. Any time you add a new row, this column will update as well!
If you like, you can use a column formula to reference multiple columns. Let's say you want to know the total cost of an item which is made up of the list price and the tax. When you choose Add column formula you can add those two columns together to get the total cost in the third column. Fun fact - in this example, the tax column is also a formula (.07*[List Price]). Coda tables are smart, and will recommend formulas based on your data. In the example below, the table intuitively knows to add row 1 List Price to row 1 Taxes to add up to row 1 Total cost.