Wall tiling is generally a simple matter of hanging the tiles starting at the centre of the wall and building outward, in a grid pattern, then trimming the tiles at the edges to fit. This is preferable to starting at one end of the wall and working across, because it ensures that the partial tiles at the edges are the same size on both ends. The cut sides of the tiles meet in a grout line in the corner.
Tile the walls on either side of the corner, hanging all the full wall tiles that will fit, working from the middle of the walls outward. On each wall, stop when you get close enough to the corner that a full row of tiles won't fit. Let the tiles set overnight.
On one wall, measure the space from the corner out to the edge of the line of full tiles. Subtract 9 mm (3/8 inch) from that measurement. Mark the measurement on a tile. Cut it on your tile cutter.
Spread tile adhesive on the back of the cut tile, using your tiling trowel. Press the tile into the space with the cut side facing the corner and the finished side facing the other tiles. Space the tile evenly with the previously set tiles -- generally, about 3 mm (1/8 inch) and leave the rest of the space between the cut side of the tile and the corner -- generally about 6 mm (1/4 inch).
Repeat for each tile on each side of the corner, until the whole corner is tiled. Let the adhesive set for a day.
Use your grout trowel to grout both walls and the corner, pressing the grout into the spaces and scraping it off the surface. Wipe up the excess grout with a dampened sponge.
Wear eye protection during the tile-cutting.