hi.
You should have an array for each line of tiles, then have a 2nd array with bools corresponding to the tiles array.
So lets say you have a 10x10 grid then you will need 10 arrays for the tiles.
Make the 1st array and call it 'row 0' (best is to start with 0 as index also start with 0)
the 1st tile should be on index 0 and the last tile on index 9.
Then make a 2nd array and call it row 0 Check)
This should be a bool array (if you want to know what is on the tile an int array might be better)
Do this for each row.
Then when you place a tower on the 3rd tile in row 0 (3rd tile will be in index 2 on the array) :
Set the bool value to true on the 'row 0 Check' on index 2.
To check if a tile is occupied, select the tile, then find it in the row arrays, then get the index and use that index to check the bool value on the 'row 0 Check'
i hope you understand what i mean.
If not, let me know and i will make a video after the new year.
Best is to use arraymaker with this, its more advanced that the included array.