Wow, broad question. I'm not so sure I know how to answer it. Being a webmaster can include everything from developing, to designing, to promoting, to managing a website. Depending on the specific model, it can encompass elements of a community, of a business, of retail/commerce ... there's just so much.

What's the basic web design knowledge?Should I know php and asp?

Web design is actually designing the look and feel of sites. PHP and ASP are two backend server-side programming languages that are used to create dynamic web applications - this is the job of the web developer. I guess the only advice I could give is to decide what type of website you want to build, and research what you need to make it a reality.

I want build game or entertainment related sites.Should I need to know them?

I think my question is too stupid.I should delete my last post

Still very broad What kind of game or entertaining site? If it is going to be Flash games, you need to know Flash. If it is going to be java games, you need to know java. And so on, and so forth.

One word of advice - don't get discouraged at first. Programming can be very hard (especially for a new programmer struggling to learn) but it can be VERY rewarding.

I'd say there's a big distinction between the webmaster, the web developer, the content provider, the editor, and all other roles for most non-trivial websites.
As the site grows the webmaster will more and more have a supervisory role as a manager with business responsibility rather than being actively involved in the development process itself.

It depends upon your interest in particular area, level of competence and skills either you want to make a career or start your own business.

Or you can be someone like me who plays every hat that exists.