Hello pedro9! Could you provide some images showing what you tried? There are many ways to do this and it will vary depending on what you are trying to achieve. As Pariah013 mentioned, you can use the OnComponentBeginOverlap to do this.
The coding will be done in the whichever blueprint you place your trigger box in. Reference the Trigger box and cast to your character. Then use the SpawnActorFroClass node to spawn whatever it is that you want to spawn. If it is a specific mesh blueprint or actor you want to spawn then you can call it in the class there. If it is just a simple mesh that already exist in the library, then you can set it like this.
Set the class for your actor as StaticMeshActor. Then get the static mesh component of that actor and set it to the mesh you want. Hope this helps.