Can I bring the girlfriend here together with the baby, and is this a long process?

There is no immigration via category by which a U.S. Lawful Permanent Resident (holder of a "Green Card') may petition for a girlfriend or boyfriend, and this is true even if the couple may have a child together, but a Permanent Resident may sponsor and petition for a spouse. When the spouse is abroad, the application process is known as "consular processing." The time for completing consular processing depends upon many factors not mentioned in your question, including the country of which your girlfriend is a national. If you soon may become eligible to apply to become a naturalized citizen, then upon succeeding with that application, and upon becoming engaged to your girlfriend, you may be able to sponsor her for a fiance visa for the purpose of coming to the U.S. to marry you within the required time, and then applying for adjustment of status. Of course, there are additional details that have an impact upon immigration eligibility. It would be wise for you and your girlfriend to consult with an immigration attorney who, after learning all of the relevant facts about each of you, could advise about immigration eligibilities, options and strategies and could represent you and her in the often complex application process.