If my boyfriend and I plan to get married, how do I legalize and start process for my boyfriend who is here on a tourist visa?

Best wishes for your plans to become married. Generally, if a foreign national entered the U.S. lawfully and with inspection, such as with a B1/B2 visitor's visa, and later marries a U.S. citizen, the couple can succeed in a marriage-based adjustment of status application process by which the foreign national spouse can become a Lawful Permanent Resident (get a "Green Card"). The process includes such things as filing a properly prepared and fully documented Petition for Alien Relative, Application for Adjustment of Status, Application for Employment Authorization Document, biographical information forms, Affidavit of Support (a joint sponsor may be needed if the U.S. citizen spouse does not have sufficient documentable income to meet the I-864P requirements), etc. A full "step-by-step" set of instructions will depend upon details applicable to each spouse. There really is no substitute for consulting with an immigration attorney who, after learning all of the relevant information, could advise about immigration eligibilities, options and strategies and could offer legal representation in the often quite complex application process.

After you get married, you guys can file an adjustment package. Forms can be found at uscis.gov website: i 130, i 485, etc.