Is it important for a online business to obtain a EIN ?

An EIN, Employer Identificatin Number, is the taxpayer identificaton by which your business will be known to the IRS, just like an individual uses a Social Security Number.  Businesses may need EIN's for many reasons, but certianly the business needs an EIN if it has employees and/or if it is taxed as a corporation or partnership.  If you are going to operate your business as a sole proprietorship and have no other employees,  you may not need an EIN.  Whether you should structure your business as a corporation, an LLC, or some other structure is a different issue.