This is the quickest but one very useful tip for Hammer map design.
When you drag a prop model into the map, it won't have any collision, so if you want heroes to walk over it or be blocked by it, you need to add a skip or clip block. You could make a very raw block like a neanderthal, but there is a better way that will maintain every edge on the model:
- Copy Paste Special (Ctrl+Shift+V with the model selected)
- Selected props -> Convert into Editable Mesh (Ctrl+Shift+T with the newly selected pasted model)
- Apply material (Shift+T)
Thanks BMD for the gyfs