ScriptName Jail
Begin gamemode
If ( GetNumKeysPressed == 2 ) player.Gotojail
endif
end

It's to see if i can get if statements working but this doesn't work.

I have found that Player.GoToJail doesn't work other than in the Script Result of a Topic Conversation
Instead, try

"PrintToConsole GetNumKeysPressed %0.0f" GetNumKeysPressed

Or something like that.

scriptname time
Begin gamemode
float time;
time = time-1
if (getkeynumpressed == 2 and time < 0 )
{
player.additem 00004330 1
time = 200
}
endif
end

this gives a time not found error and i'm not sure if my other code is correct.

declare your variables before the Begin block and the syntax of your code will not be compile in the CS
try this

scriptname timefloat timebegin gamemode	set time to time - 1	if getkeynumpressed == 2 && time < 0		player.additem 00004330 1		set time to 200	endifend

There's a lot of Scripting tutorials here: http://cs.elderscrolls.com/index.php/Portal:Scripting

You can use the editorID name instead of the formID code, it is actually better that way since your scripts will gain clarity.
Also, OBSE has its own commands for variable assignment, which will debug info to the console if something goes wrong. Instead of 'set ... to ...', get used to 'let ... := ...', and you won't ever want to go back (I swear!).
And you can even use mathematical signs instead of the : , so you can simplify things like

set time to time - 1

to

let time -= 1

Agreed with migck.
But I didn't know you could do -= with Let.
I assume you can do +=, --, and ++, as well.

http://obse.silverlock.org/obse_command_doc.html#OBSE_Expressions

I want to be able to make 5 daedaric arrows after 200 frames when pressing Q but it doesn't work. The editor thinks it's fine though.

scriptname time
float time
begin gamemode
let time -= 1
if getkeypress 16 && time < 0
player.additem 0001EFD3 5
set time to 200
endif
end

If you want to have this executed after exactly 200 frames, you're assuming that your script will run every single frame.
This is only true for object type scripts, which are attached to a base object. As long as a reference of this object is loaded ingame (i.e. it is "physically" present in a loaded cell), the script will be run for every frame as expected.
Once you leave the cell, execution will be suspended, unless you haven't unchecked the "No low-level processing" flag for that specific reference.

Be aware that such "run-every-frame" code can put heavy load on your CPU and therefore is not a good practice (unless explicitely needed).

In contrary, quest type scripts (attached to a quest) will run in a 5 seconds interval by default (which can be changed by setting a value for fQuestDelayTime). This is much more recommended. As the 5 sec might cause problems with keyPressed detection, you should consider placing your code in a quest script anyway, but changing fQuestDelayTime to a lower value, such as 0.2 or 0.1.

Example:

ScriptName MyQuestScriptfloat fQuestDelayTimeshort doOnceshort questEndedbegin gameMode  if doOnce == 0	set fQuestDelayTime to 0.2	set doOnce to 1  endif  [... your key detection code goes here ...]end

As a good practise, once your "run-very-often" logic isn't needed anymore (e.g. if the parent quest is completed), try to change fQuestDelayTime back to normal (i.e. a value of 5 or higher).