Starting from top left you must identify what country borders what either horizontally or vertically and select the tile that borders the previous one you selected. You continue until you get an answer on the right side.
I am counting the Oresund Bridge as a border
If this confuses you, I'm sorry. A more detailed explanation in comments
To solve this, you must start from the top left and click the country( either horizontally or vertically ) that borders with the previous one. If you get squares, it is because you head down then right then up. Keep going until you get to one of the countries on the far right.