You do not need an account or a desktop engine. Set the position—or start from the beginning—and the site shows the strongest move, a short reason, and how likely each side is to win.
That helps when you review a game, try an opening line, or check a tactic from a book. The best line is not a mystery: you see it on the board with alternative moves ranked behind it.
Because Stockfish runs locally, the position stays on your device. Open the board, make a move, and read why the engine likes it.