Collisions are handled by Unity Collider modules; Box Collider, Capsule Collider, Sphere Collider or Mesh Collider
See here:
https://docs.unity3d.com/Manual/CollidersOverview.htmlI'm having a hard time judging what level you are on and what you need to know or not. I don't know if you need to maybe watch a YouTube tutorial on colliders and setting them to triggers or not.
Basically the collider is the way you can bump in to something. If the object has a collider and a Rigidbody, you will be able to push it (if it's not set to kinematic). You use that regular collider and add a
second collider which is a little larger (so it will be hit before the one used to push the object), with the second one set to be a Trigger. This means the second collider is a like a ghost you can pass through, but you can use it to register if something Enters, Exits, or Stays in that trigger.
As mentioned previously, you do this via the Trigger Event action. You set what object you are watching, if it's enter, stay, or exit, and then also (for your case) set what Tag the other colliding object must have to be valid.