Try to empty the playing area completely, by removing connected groups of two or more squares of the same color. Then try to score as much as possible, by removing large groups at a time instead of small ones.
On a touch screen, a tap does what a click does, and a long press what a right-click does (more ways to right-click).
Click on a colored square to highlight the rest of its connected group. The status line will print the number of squares selected, and the score you would gain by removing them. Click again to remove the group; other squares will fall down to fill the space, and if you empty a whole column then the other columns will move left to close the gap. You cannot remove a single isolated square: try to avoid dead-end positions where all remaining squares are isolated.
Right-click a highlighted group to let go of it without removing it.
With the keyboard, the arrow keys move a cursor around the grid, wrapping round at the edges. Enter highlights the group under the cursor and removes it on a second press; Space highlights it, and lets go of it on a second press.
Hint shows a group to remove next, one that still leaves a board that can be cleared. It searches for a way to clear the board from wherever you are, so it carries on from your own moves too. It is about clearing the board, not about the score: the group it picks is not always the one that scores the most.
The step says why it picked that group where it can show it. A square that is the last of its color can never be removed, so a hint warns you off a group whose removal would leave one, or would leave no two squares of one color side by side. Where it has checked every other group, it says which of them could also go next. Otherwise it points out a square with no partner of its color beside it that the removal brings one to.
If no way to clear the board is left, the hint says so, and the thing to do is undo. Show solution clears the board for you.
These parameters are available from the ‘Custom type…’ option on the ‘Type’ menu.