Press the left mouse button to start the match. Now move the mouse on identical adjacent alphabets (Horizontally, vertically or diagonally). Select at least 3 or more alphabets. Release the mouse to let the match happen. This will merge the selected alphabet letters and creates a one new letter which is the next to the selected.
For example if you select 3 or more than 3 blocks labelled with 'A', the resulting letter will be the B. Keep matching and merging the alphabets until you get the Z.
In easy mode you can upgrade to higher alphabets easily, where the normal and hard mode upgrade takes more work.