Your question is vague, but whether it's a console game or a game using a graphics library, you'd need to have some sort of AI for the enemy. Try thinking about how to make the enemy go closer to the player each iteration, being grid-based makes this easier to calculate*. Then, for every iteration that the enemy is within 1 grid tile to the player, the player takes a certain amount of damage.
*ex: if (player's x coordinate is larger than the enemy's x coordinate), have the enemy shift over 1 right, else have the enemy shift over 1 left. Same for y axis.
@Ganado sorry its not console game haha.. the game is, like text ,you will choose in between battle or shop then if battle you will choose between attack and run