Well a design is obviously very important and good coding too. If you have Photoshop or something similar you might be able to create your own design but honestly if you want a good design it takes alot of practice to be able to do it yourself. Just find a cheap but good designer. There are plenty of them on this site that would be willing to design for you at a good price.
After the design you need to code the design. Again, coding is not something you can learn properly overnight and the skill of coding required all depends on the complexity of the design. There are loads of cheap but good coders on this site so I would advise you to look for one.
The basic coding is HTML and CSS which stick your design together in a format that browsers can read and display but remember they are only used to stick your site together. You must know a programming language called PHP to make your site dynamic. There are many other programming languages out there but PHP is one of the easiest and it is easiest to find a PHP programmer. Is that all you need to know?