(but not on the ceiling). The length of his room is 10 feet the width is 14 feet and the height is 12 feet. If each tile is 1 foot long and 1 foot wide how many tiles does he need?

Two walls are 14 ft x 12 ft = 168 square ft (or tiles) each wall or 2*168 = 336 for both walls.

Two walls are 10 ft x 12 ft = 120 square ft (or tiles) each wall or 2*120 = 240 for both walls.

336 + 240 = 576.

So you may need 578 tiles to cover all four walls.

In reality, the thickness of the tile at the corner reduces the amount of tile needed at the adjacent wall by the amount of the thickness. I.e. if the tile is a quarter inch thick and goes all the way to the wall, than its adjoining wall will need 1/4 inch less tile, or 1/2 inch less tile from both sides.

Most tile installations include a separation of about 1/8 to 1/4 inch between tiles which is filled with grout. That also reduces the total number of tiles needed.

Since during installation, you don't know exactly what will happen, and you need to consider the possibility of mishaps such as dropping tiles and breaking or mis-cutting, it is a good idea to get extra tiles at the beginning and return excess tiles when done, or keep a few for future replacement.