You don't have to register to get access, just select "Play as Guest" to get straight to the puzzles. Registration does give you the option of playing on Puzzle Daze at Puzzle Daze and of upgrading to Premium Membership which gets you full access to the puzzle archive that stretches back to the 1st of January 2007
Basic Controls (Sudoku, Kakuro, Futoshiki): Left click a box to enter a number. Double-click (or shift-click) to enter a possible number, enter the number again to clear it. Press 0 while a box is selected to completely clear the box.
Basic Controls (Nonogram): Left click to mark a box as solid. Shift click to mark a box as a space. Drag select to mark multiple boxes as solid/space. Clicking again clears a box.