You get six chances to guess the secret word. It is one of about 2500 commonly-used English words with exactly 5 letters. Just type the word and hit RETURN/ENTER to see if you guessed it correctly. If you had any letters in the correct position, they will be highlighted as green. If you guessed a letter that is in the secret word, but in the wrong position, it will be yellow. Any letters that aren't highlighted are not in the secret word, so you can eliminate those from later guesses.
For more information and the code (which also can be built for the Commodore 64), check out the repo on GitHub: https://github.com/SlithyMatt/cbm-wordslide
If you see any apparent bugs, or words that should or shouldn't be included in the list, please enter an issue on GitHub, or a pull request with your own fix -- adding or removing words from the list (2500words.txt) is trivial, and an easy way to contribute to this project!