Formulas allow you to compute a value in each record based on other cells in that same record. For example, if you have a table of product orders, you can create a field that computes the Total Cost for each record based on the Price and Quantity.
To configure a formula, select the Formula type from the field configuration menu. From there, you can enter the formula into the text box as you would in a spreadsheet, except you use the names of fields instead of cell ranges. A formula can be composed of functions (e.g. SUM, CONCATENATE), operators (e.g. +, -, *, /, &), and other fields from the same table.
When you start entering your formula, you will see suggestions of fields and functions you can use in the formula.
If your formula will result in a numerical output, you have the option of formatting the formula's result as a decimal, an integer, a currency, a percent, or a time duration. Additionally, for decimals, currencies, and percentages, you can adjust the precision.
For a complete reference of formula functions and operators, please refer to the Formula Field Reference.