Ok umm...

I set a blue portal, inactive, and named it BluePortal01.

Then I made a trigger somewhere, trigger_once, and I made the output:

OnStartTouch > BluePortal01 > SetActivatedState

I tried that ingame, there is not effect.

What am I doing wrong?

Try making a trigger_multiple, but under the flags set it to "trigger once" or words meaning the same effect.

It should have worked with a trigger_once, but hammer does say to use trigger_multiple for even single triggers.

I changed it to trigger multiple, and set the thingy to -1 (was originally 1). I think you meant that instead of something in the flags, because the flags doesn't have trigger once or something related.

Anyway, it still doesn't work.

I walked passed it, my portal did not open.

EDIT:
HAHA
never mind.

It works

You have to set the Perimeter Override to 1

You tried just setoutputstate? Ahh Yeh usually they have a parameter, only one that doesnt need it is enable/disable.

Also how do you apply portals easily with the entity? I can never rotate the red box, I have to move the "origination" like line which really is hard to make it perfect lol.

You must have at least one other orange portal in the map. If you don't the blue portal may not be visible at all.

For the portal to turn off and on you need to add to that out put a parameter of 1 (on) or 0 (off).

If all else fails have both portals open but add a Logic_Relay to tell the portals to turn off at the start of the level.

Edit: Darn you beat me to it . Nevermind

That is Parameter Override by the way, not Perimeter.