The difficulty slider controlls how constrained the mine placement is. Easy should require no brainpower. Hard should be harder. Unlocked places no constraints on mine placement which may result in unsolvable games.
Note: "Hard" difficulty does not guarantee a harder game, but it simply allows the generator to make one that is.
Shows you which cells are being counted towards the mine count and lets you click to open all neighbors of a cell.
The highlight assist will tell you if the amount of flags around a cell matches the number on the cell itself. This can help you focus on performing logical deduction without worrying about making silly mistakes.
The shape settings are experimental and are likely to break in many unexpected ways. This may include the game crashing, freezing up, and more.