We play it by placing the tetromino posted by the user above somewhere on the grid. Obviously as near the bottom as possible, and in an attempt to make horizontal lines.
When a line is made, that line is deleted, and a new empty line is added at the top of the grid.
Posting form should be the previously posted grid copy/pasted, the new tetromino added in, possibly a line deleted and a new one added, and then a new tetromino for the next user to place.
That brick doesn't exist in the originl Tetris? And you forgot a +... Uhm, I'll just place a ++++, since that's the closest to a +++. (Yes, rotation is allowed.) Meaning I could make a line. Yay.