The object in Parks is to place 2 trees in each colored region. Trees cannot touch - not even diagonally. Also, 2 trees must be placed in each row and column.
For the smaller grids, like the one pictured above, you must place 1 tree in each column, row & region.
About a year and a half ago I reviewed Twin Beams, which is basically the same concept. Click here to read that.
Parks Season is a fine set of puzzles, but I must confess that Twin Beams is more polished. On the plus side, Parks Seasons has the very easy puzzles for novice puzzlers.