Use google, dribbble, freepik, behance, or any other platform.
Important: copyrights are important!
Let's break it down...
Photoshop
Measure element sizes, positions, pick colors
(This is a step you go back to all the time as you work)
Then, start to code...
codepen
Codepen is a free front-end playground where you can build small demos, supports HTML, CSS and JavaScript
(you can use plugins, libraries, preprocessors, etc).