The most current tax law can be found on the IRS site along with links to frequently requested forms (W4, W9, SS4 etc.)
The Small Business Administration site provides a wealth of information on starting a new business, from planning your business to where to apply for financial assistance. You will also find links to local resources.
Current state tax laws can be found and returns can be filed on line though these state links.
Click on the link to The Washington State Department of Licensing site to file for a Master Business License or to renew your business or professional license on line.