Do one thing, In starting you should open a good website means of any brand and for practice get the screenshot of that website and then simply trace that in photoshop. After some time you will start learning the way of creating things. This will help you very much..
first start learning how to handle photoshop. then start to create your own designs and try to get as much feedback as you can. during the time you work on your webdesign skills you should also start learning html/css when you're done with this (which will take you some time) go on and start learning how to code your designs for certain scripts/cms