The Parameters dialog appears after the Add condition or action dialog, or when editing a condition or action. It allows you to enter parameters such as the X and Y co-ordinate for the Sprite object's Set Position action (shown below). It does not appear for conditions or actions which do not use any parameters, such as the Destroy action. Expressions can be entered for parameters, which can be anything from a simple value to a sophisticated mathematical calculation.
The Expressions panel appears next to the Parameters dialog providing a list of all the expressions you can enter. By default the Expressions panel is faded out unless you hover the mouse over it. It can also be hidden or shown by pressing F4.
Use the Expressions panel to locate system expressions, object expressions, behavior expressions, global and local variables and instance variables. Alternatively you can use autocomplete: just start typing, and a list of all the options appears. Additionally if you type as far as the dot in an object expression (e.g. Sprite.) a list of all the object's expressions appears, shown below. This also appears after the dot when entering a behavior expression (e.g. Sprite.8Direction.). Use the Up and Down arrows to pick an item in the suggestions list, and press Enter to insert it. This can help you enter expressions much more quickly.
Some expressions also show tips to help you remember how to use the expression, shown below. This appears when you type the open bracket ( for the expression. This is most useful for System expressions which tend to have multiple parameters.
Press Tab to move to the next parameter or Shift + Tab to move to the previous. Enter is also a shortcut to press Done (you may have to press Enter twice if autocomplete is showing: once to choose the autocomplete entry, and again to close the dialog).