Are you thinking about changing the layout of your Island? Do you want to move your buildings around? It's simple, just hold your finger over a building until it hovers above the ground.
Then drag it to its new position and tap the green check button to set it down there.

Note that buildings should be connected to a road wherever they are.
You can also rotate the building by tapping the orange arrow button.

If you place a building on a site overgrown with weeds, the game will offer you to clear it for energy.