Row of four cards (A,B,C and D) should be built in the center of the table. On your turn you can play one of your 6 handcards. Start a row with an A or build on en existing row. On the card there are colored lines. A card can only be added if it has the same color as the last card of the row.
There are also jokers.
The player laying a D card gets the row as points and a player who can exchange a joker get the point for the exchanged card.
This is branded with the sheperd dog "Rex" from the TV show "Kommissar Rex"