So, where did that score come from?
The main word gets its new letter bonuses and word multipliers. Any little crossing words are scored separately. If a new tile lands on a bonus square, that bonus can help both words on that turn.
Before you play, check the placement list. Row 1 starts at the top and column 1 starts at the left. Blank tiles become whichever letter you need, but stubbornly remain worth zero.
How GRATER gets to 30
In our example, GRATER runs across row 12. The G lands on a triple-word square and the T lands on a double-letter square. That makes 10 points for the letters, then the triple-word square does its thing: 30.
Try it yourself →