MyBB Community Forums

I'd like construct my forum but I don't know how to make a header like my image that attached ? where should i start with it ? thanks in advance.

The hardest parts of this would be the positioning (look at this, this, and this to learn about positioning, as well as other links in the sidebar at that site) and the images. The images you will have to learn. The rounded corners don't need to be done in an image editor, just use the Border Radius (rounded corners) property and you will be set. The rest is just simple HTML. Section each part off to make it easier on yourself; for example the "Community Beta" bar and down should be "navigation", the Sign Out through MyEC21 should be "links" or something, etc.