I am wondering if it's possible to stick the orange plane on the face made by the three columns? I tried with the tutorials showing how to snap objects together. but the plane is never parallel. Thanks
Snap to Face will allow you to project the elements onto other faces, similar to what a shrinkwrap modifier would do when set to axis projection mode. However, if you want to snap every vertex onto the target, there is two buttons to enable. Face Snapping (marked on the left), and project individual, marked on the right:
Then, a source geometry which looks like this...
...would snap like this:
Align rotation in Face snapping
Blender has a tool that is capable of aligning the local axis of an object to the target surface normal. You can find that right next to the snap settings:
Unluckly, as I said, it works with objects, so it's not available in edit mode, and it requires the local axis of the plane object to be already aligned with the plane faces's. So, in your particular case, you should separate (P) the plane mesh and work on the orientation before snapping to the surface (if your plane has a "random" orientation, you can use, for example, the Precise Align add-on, as shown here: https://blender.stackexchange.com/a/36787/15140.)