Starting a new job

I just got hired for a job and it was an immediate hire role. I won't be able to give my 2 weeks notice at my current job and would live any advise on what to tell my boss when I go in again. I don't want to leave on bad terms, but the only days I have on my schedule are the days that they need me at my new job. I am going from retail to warehouse work and I have never had to do this before. Any help would be wonderful.