1a - Hit Points [number box]: This value should be obvious enough; it is the normal, or "default" number of hit points a unit has. Changing it is as simple as putting in another number.
1b - Hit Points [small number box]: The purpose of this little value is still unknown. I wouldn't mess with it too much.
2a - Shields [number box]: This value is just like the hit points value, only it tells Starcraft how much shields to give this unit. You should check 2b for a unit to have shields first. [See 2b]
2b - Shields [check box]: Check this box to give the unit shields. Any unit may have shields, not just Protoss units. The amount of shields the unit gets is the number in 2a. [See 2a]
3 - Sight [number box]: This value tells Starcraft how far the unit can see (or, in other words, how much Fog of War it clears up). The higher the value, the farther the unit can see. The max is 12.
4 - Armor Upgrade Group [pull down menu]: This pull down menu will give you a list of all the "armor types." For example, Infantry (T) is Terran Infantry Armor, Vehicle (T) is Terran Vehicle Armor, Ground (Z) is Zerg Ground Carapace, and Ground (P) is Protoss Ground Armor. This value tells Starcraft what armor "upgrade group" to put the unit in. For example, a unit in the Infantry (T) armor group will get its armor upgraded when you upgrade armor for your Terran Infantry units at an Engineering Bay.
5 - Amount [number box]: This value is the amount of armor a unit has (before upgrading).
6 - Build [number box]: This value tells Starcraft how many points to award a player for each of this unit he/she builds or trains. It is recorded in the general Unit score after a game is complete.
7 - Destroy [number box]: This value tells Starcraft how many points to award a player for each time he/she kills or razes this unit. It is recorded in the general Unit score after a game is complete and is also the number of "kill point" you get if you are displaying a kill score leaderboard.
8 - Time [number box]: This value is how long it takes to build/train the unit. The higher the value, the longer it will take.
9 - Minerals [number box]: This value is the mineral cost of the unit.
10 - Gas [number box]: This value is the gas cost of the unit.
11 - Space [number box]: This value tells Starcraft how much space this unit will take up in a transport/bunker. For example, a value of 1 makes this unit take up one little box of transport space like a normal marine. 2 makes it like a normal hydralisk. 4 makes it a "big" unit, like a tank. Flying units generally have a value of 255 -- meaning "I can't go in transports." =)
12 - Supply Required [pull down menu]: This value is how much "food" (supply/control/psi) the unit uses up. 49.5 is the maximum and 0 is the minimum. Units like the zergling only use up .5 ("half") food. Any unit can do similarly though (as well as having some strange improper fractions like 4.5).
13 - Size Menu [pull down menu]: This value determines what "size" unit it is. This does not actually change how it looks. The main thing it effects is how much damage it receives when it is attacked by weapons that deal concussive or explosive damage. [See the Weapons section for more detail]
14 - Width [number box]: I am not sure at this time.
15 - Height [number box]: I am not sure at this time.
16 - Circle X [number box]: I am not sure at this time.
17 - Circle Y [number box]: I am not sure at this time.
18 - Movement [pull down menu]: This value tells Starcraft how this unit moves around. Even though there are 5 different values, only 3 are actually used. Walk means the unit does some leg action when it moves from one place to another (in other words, it "walks" or has an animated moving stance). Creep means the unit moves only on zerg creep like eggs and larva. None is used for all the units like "glide" around (i.e., all flying units and hovering ones like the vulture). The other values are not used and I suggest you don't use them.
19 - Anim Height [number box]: This value is the Animation Height of the unit. This basically tells Starcraft what "level" to place the unit on. For example, ground units generally have an anim height of 4, while air units have an animation height of 18. The values go from 1-19, each being one layer higher than the other. The lower layers are "below" ground (move under everything), the semi-low layers are normal ground, and the higher values are for flying units. This may be a little confusing but if you play around with it, its not so tough. Despite how it seems, this value rarely crashes Starcraft. For a full list for Anim Height values, see King Arthur's SPEC sheet.
20 - Room [number box]: This value is the number of units that can "go into" this unit. For example, Transports can hold 8 and bunkers can hold 4 (depending on units' space, of course). [See 11] While you can give any unit Room, it will not do anything unless a few other values are changed (notably in the AI/Orders section). Though, even if you achieve the ability to "load" units into a non-transport, non-bunker unit (let's say a wraith), there is no way you can get those units back out (unload). It is possible to have a transport (or a bunker) have more than 8 room, but you will not be able to see their wireframes in the trasnport (because it will already bee full). That may also crash Starcraft. I suggest only modifying the value for transports and bunkers from 0 to 8.
21 - Food x2 [number box]: This value is how much "food" (supply/control/psi) the unit provides the player with. The type of food it produces depends on its group. [See the StarEdit section] The number you put here is actually 2 times the actual food amount you will see in the actual game. For example, if you put a value of 20, it will produce 10 food. As far as I know, any unit can be given food (it will also automatically display your food statistics in the control bar when selected). If you give a unit 0 food (i.e., a command center), it will no longer display the food statistics when you select it.