Choose a word to be the answer and store it in a variable. (We will make it a random word later, but during testing phases it's easier if you know exactly what the answer is.)
Append the divs to the page. (Tip: to get the line at the bottom, try using borderBottom.)
Using a <canvas> tag, "draw" the body of the Hang Man and the stand. (Tip: The w3schools page about canvas tags is very useful!)
When one of the letter buttons is clicked, disable it. If it is in the word, have the letter appear on the correct line.
If the letter isn't in the word, have the first body part appear in the canvas. (If the user guesses a second wrong letter, the second body part should appear, after a third wrong letter the third body part should appear, etc.)
If the user loses (all the body parts appear before they guess the word) have the rest of the letters appear in red and disable all the letter buttons.
Once the user has won or lost, have a "New Game" button appear.
Create an array with a bunch of words. Instead of having your word be the answer every time, make it choose a word from the array at random.
Create a two player mode where the user can input a word that is the answer. Let the user begin the game by selecting either one player or two player.
Keep working until you're happy with your game. You could add different levels or themes to the One Player mode, give the Hang Man fun accessories, etc. The possibilities are endless!