Whether you are incorporated or just a dba, you will need a tax ID number from the IRS for a host of reasons- opening a bank account, collecting payments from customers, tracking and reporting payroll under the business' name, to name a few.
If you are forming an LLC or an S Corp, you can get the tax ID number either before or after you incorporate. You just want to make sure the name you type in on the IRS site exactly matches the name you ultimately chose for the business.
Getting the number is simple. You can use this IRS.gov link and follow the steps in the form. You will get an electronic confirmation immediately with the number- make sure you save that screenshot, because the official letter with the number may not arrive for several weeks.
Note: if you search in google or other search engine for "get a federal EIN" or "Get a tax ID" you will first see ads with urls that suggest some affiliation with the IRS. Do not use these links- they will charge you a fee for applying for the EIN. This process is 100% free if you do it directly at irs.gov, and it is simple to do.