Fifteen Blocks is a classic game originally played with physical blocks you slide around on a tray. The goal is to arrange the blocks in numerical order from 1 to 15.
Start by shuffling the tiles. Then drag a tile next to the empty space into it, just as you would slide a real block across a tray. Clicking the tile works too.
It's easy to get the first couple of rows in place, but the last few tiles can be tricky.
On a computer, try using arrow keys.