A net of a cube is the flat shape you get by cutting the cube along some of its edges and unfolding it onto a plane — six squares joined edge to edge, which can be folded back up to give the cube.
Six squares: a vertical strip of four, with one square on each side of the third square from the top.
Two things are needed. There must be exactly six squares, because a cube has six faces; and they must be joined so that folding brings every free edge against exactly one other free edge, with no two faces landing on top of each other.
Tip: When you actually build one, add small flaps on alternate free edges so you can glue them down — but the flaps are not part of the net. The net is only the unfolded surface itself.
Q2.
Visualise how it can be folded to form a cube.
Answer
Fold along every internal line, all in the same direction, keeping one square flat on the table.
Keep the third square of the long strip (the one with a neighbour on each side) flat — this becomes the base.
Fold the left and right squares up. They become two opposite walls.
Fold the square below the base up. It becomes a third wall.
Fold the strip going upwards: the square just above the base becomes the fourth wall, and the one above that folds over to become the lid.
How to check without cutting: in a finished cube, opposite faces never touch. In this net, take the vertical strip of four squares — folding a strip of four wraps it right round the cube, so squares 1 and 3 are opposite, and so are 2 and 4. The two side squares are the remaining pair. Three pairs, six faces, nothing repeated: it folds.