Settings are saved one at a time, inline:

1. Open Business Settings > Configuration and click the Order tab you need.
2. In the Value column, click the current value (it shows Click to set when empty and a pencil icon appears on hover).
3. For text settings type the new value; for drop-down settings pick an option from the searchable list.
4. Press the orange check mark to save or the X to cancel.

The change is stored immediately and written to the activity log. There is no page-wide Save button - each row saves itself. Image settings work differently: choosing a file uploads it straight away (see the next question).