What are the rules of 10x10 Draughts? How many pieces are on each side?
Each player starts with 20 pieces.

From Wikipedia:


  The gameboard comprises 10×10 squares in alternating dark and light colours, of which only the 50 dark squares are used. Each player has 20 pieces, light for one player and dark for the other, at opposite sides of the board.


You use the first 4 rows (with 5 squares per row being used).