The Instruction list shows the value of each parameter in each instruction. As you click on this list, the selected Instruction will be shown in the edit boxes on the right. Different boxes become visible for different instruction types. These 2 boxes are always available, as all instructions require a Time parameter (shown in "raw" format with the conversion to seconds above) and an Instruction type. There are several options in the Instruction list which are unused and so are represented only by numbers. Beneath these boxes is the Time Adjustment Increment: From here you can select the increment that the Time value will change by in the Time spin box. The options are shown in seconds, i.e. 1/25 sec = 1 "raw" unit.

The Instruction List is also useful for deleting Instructions, changing their sequence, and tweaking their parameters. You can change the sequence of events using the  buttons.
 

Adjust time for all following instructions
Selecting this option will mean that increasing or decreasing the Time of an instruction will adjust the Time for all of the following instructions by the same increment, allowing you to 'slide' the rest of the briefing back and forth to adjust the length of time between events.
 

Unknowns
The effects of these three parameters is unknown, but you can get away with leaving them all as zero.
 

Map Tags
Map Tags are short descriptions, usually FG names, that will be placed on the Briefing Map itself, among the icons.

Briefing Text
These are the longer sections which will describe the mission in detail, and appear underneath the Map. AlliED uses the first string in this list as the caption in the main window, so it's a good idea to make the first string your mission title.

You can also highlight a section of a string by enclosing it in [ ] brackets, e.g.: 

"This is [highlighted] text" will appear as:
 

This is highlighted text