The first tile is already a path, you shouldn't have to click it, not sure what's happening there.
You can remove path tiles by toggling the path mode (bottom left button).
I thoughr the items were pretty intuitive but I guess not:
defuse/detect - click the button > click the tile you want to use it on
fix - click the button > select the tank you want to fix (tank must have hit a mine already)
reroll - click the button (didn't get round to adding a confimation prompt)
Thanks for playing.