De and Wo

I am wondering, why is it , "shingou DE hidari ni magatte kudasai" and not "shingou WO hidari ni magatte kudasai"? Because Wo is used in "kousaten WO migi ni magatte kudasai", why is that?

And also why if it isn't De, why is it? Cause isn't hidari ni magatte kudasai, and activity hence De describe the place where it happen? Please help me with this, yoroshiku onegaishimasu!

"Shingou DE..." is like "at (the location of) the traffic light." You look up at the light that marks the location.

"Kousaten WO...": "kousaten" is part of the road, you go through the road/crossing. This is the same use of "wo" as in "Maiasa kouen wo sanpo shimasu." (I take a walk around/through the park every morning.)

Hmmm, I'm still not
very clear about the difference of de and wo in this context

De is used to mark the location at which the action is occurring. Wo is used to mark a location that is being travelled through.
E.g. 公園で歩いています｡
Lit. "In the park, I'm walking"
公園を歩いています｡
"I'm walking through the park"

So, when talking about turning at the corner you need to specify the location of that turning action, i.e. the corner.

Oh and 'ni' is only for expressing a location in terms of direction or existing. It can't be used to specify the location of an action.
公園にいます。
I'm in the park
公園でサッカーをしています｡
I'm playing soccer in the park.