How can I put it next to entry blog on right without using margin:-3900px;?

Well, you can place two divs side by side if you use this CSS rule on both and the widths combined aren't too wide for the containing element.

display: inline-block;

Other use float: right; on the div you want on the right. Float can have some unexpected effects though depending on the page structure.

I wouldnt suggest that you use the margin properties for that purpose. The problem with using the margin property in this way is that you'll have all sorts of unexpected display issues (elements shifting) especially when you do not have a "wrapper" div that is centered in the middle of the page.

You can have divs line up against each other traditionally using the float property such as:

#div1 {float:left;width:50%}
#div2 {float:right:width:50%}

Take a look at my website I used float an not results just this mess Click Here
Thank you for your help