How Do I Make Obstacles to help me in prototyping?

What I mean by that are ramps, bridges, and other physical obstacles to help me test out the character controller. I don't know how to make them. Do I need to use blender? Can it be made in unity itself? I'm clueless.

 

Blender is one way. The easiest thing to do would probably be to install ProBuilder (Free) from the package manager. It's a little bit easier than using Blender because you can edit geometry directly in the Unity editor.

Another alternative is to use an asset pack like: https://assetstore.unity.com/packages/3d/props/exterior/polygon-prototype-pack-137126

 

I would say use blender to do the finalised ingame versions of those obstacles. But as kdgalla mentioned, ProBuilder might be simpler for that, especially if you are making props, for play testing character interactions with objects in the enviroment .