This is a type of logic puzzle known as a battleship puzzle. The ships must be placed in the grid so that no two ships are adjacent, even diagonally, and so that each number tells the number of ship segments in that row or column. The ships to use are shown below the grid. This particular puzzle has one more submarine (one-square ship) than usual for this size of puzzle, but that does not affect the logic.
This is not a particularly difficult puzzle for experienced battleship solvers, and hopefully served as a good introduction to the type for solvers who have not seen it before. The completed grid looks like this:
Read from top to bottom, the five submarines spell out the nautical word AHOYS, the answer to this puzzle.