Answer 1

With html you can add elements like paragraph for text, img for images...
For this kind of app you need javascript, and if you wish to have UI(interface) then you need html and css.

To make this possible, you can make database of all characters for your password, then select random character from it Math.random() can help you with getting random number: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/random

You also need to decide length of password will it be fixed length like 7 characters for example, or password may be between 5-20 for example. If so you need additional random number.

Some ideas: take user input, to control length of password, and possible strength.
if strength is strong then add special characters for example, for medium use letters and numbers, for low use just letters.
Make sure generated password will have at least 1 of each character category, if it is strong password.
Show generated password for user to copy/paste as result.

Answer 2

Here is some sites, use it for inspiration:
https://www.lastpass.com/features/password-generator#generatorTool

https://delinea.com/resources/password-generator-it-tool

https://www.dashlane.com/features/password-generator