Right click or right click drag to delete paths of the type currently selected. There is a help section in the main menu, and in the top right of the levels there is a help icon for easy access to the same information, so you don't have to go all the way back to the main menu if you forget something.
I wanted to give the players more control when deleting things, that's why it only deletes the same type. I'm already thinking of different ideas to solve this issue, and I'll probably implement most of them like a toggle to enter a delete mode where you can clear anything like in the level builder, and maybe people would find an undo button more intuitive.
Don't worry, you're not the only one who got confused by that! I got too focused on clearing clutter (you can tell if you look at the settings) that I hid the controls in the help section which nobody actually reads. I think I need to come up with an interactive tutorial after the game jam, as well as implement the other ideas.
The placing sound was made using standard cards and some audacity effects, very happy with that sound.
Thank you for playing!