Tile may be installed with mastic or thinset adhesives. Both are spread with the straight edge of a trowel and then combed with a notched trowel. Use a square-notched trowel for large tile and a V-trowel for small tile. The larger and thicker the tile, the larger the notches should be. To test the size of the combed ridges, as well as the consistency of the adhesive mix, press down on a test tile, remove it, and inspect the back. The back should be fully covered with adhesive.
When tiles break, it's often due to substrate or installation problems. The video below shows the accepted way to trowel out adhesive to ensure adequate coverage. Troweling in swirls (at one time considered good practice and still common in the field) can create voids that leaves the tile unsupported. This is not recommended practice, particularly for large format floor tiles.