Learn Finnish: Sotilas putosi shakkilaudalta. - The pawn fell from the chessboard.

In Finnish, the chess piece we call a "pawn" in English is called a sotilas (literally "soldier"). The context of shakkilaudalta (from the chessboard) makes it clear that we are talking about a chess game rather than a real military soldier.

What is the dictionary form of putosi, and why does it have a "t" instead of a "d"?

The dictionary form is pudota (to fall). This is a type 4 verb, which undergoes reverse consonant gradation. The weak grade "d" in the dictionary form changes to the strong grade "t" when conjugated, as seen in this third-person past tense form putosi.

Why is the ending -lta used for "from" in shakkilaudalta instead of -sta?

The noun ends in lauta (board). In Finnish, you use the outer local cases for flat surfaces, like being "on" a table or a board. Since the pawn was on top of the board and is moving away from it, we use the ablative case -lta (from on top of). If it were falling out from inside a box, you would use the elative case -sta (from inside of).

Why does the "t" in shakkilauta change to a "d" in shakkilaudalta?

Adding the -lta ending closes the final syllable (lau-dal-ta). In Finnish, a closed syllable usually triggers standard consonant gradation, which weakens the strong "t" in the base word lauta to a "d" in laudalta.