Interviewers want to know that you will stay with their company long-term if you are hired, and now is the time to assure them that you will be on their team long-term.
If the short employment was due to summer work while you were a student, that's no problem! Simply tell the employer that it was an agreed upon summer job only while you were in school.
Keeping things positive is key! Be sure to only talk about your past companies in a positive manner recognizing what wasn't a good fit for you instead. You might share that you relocated unexpectedly due to your spouse's job which resulted in the short duration of employment. You might share that you were offered a better position elsewhere that you just couldn't pass up! Perhaps you will share that you realized you didn't enjoy working in that call center job you recently accepted because it lacked face-to-face interaction, so you decided to leave the job to go back to cashiering because you know that you love it. Be candid with the interviewer sharing why you were only in your past job for the shorter duration of time.