what is different between design view and live view?

i developed a webpage in visual studio 2010 by c# and asp.net Langs . when i run my page , UI is OK in browsers like Firefox and IE but when i look at aspx file in design view i see disordered in HTML tags. i saw this cause in another projects (i have no java script in UI) or in adobe Dreamweaver in design view UI elements are      disordered but in live view is OK or in browsers are OK why? my question is must we fix UI disordered or fix problems at first in design view after in live view to have not any bugs after published it in any browsers or not?or this is not important?
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