This quest is triggered as you complete Out of Time. You'll also have the option of picking up a laser musket, a weapon that we recommend for an upcoming event. It's sitting on the ground outside in front of the steps that lead up to the Museum of Freedom.
Enter the museum and fight your way past the Raiders scattered throughout the building. Use the myriad rooms as cover, flanking and to make brief retreats should you need to heal.
After the shootout, meet up with the Minutemen, particularly Preston Garvey. He will advise you to use the Power Armor, so follow the waypoints and a handful of objectives to get armed and suited up.
You'll be be asked to clear Concord of its hostiles. That includes some Raiders and the Deathclaw. By now you should have enough weapons to take it out. Use the urban surroundings to periodically heal and possibly flank the Deathclaw.
Once it's down, report to Preston back in the museum. He'll lead his crew to Sanctuary Hills — your old neighborhood. You're free to go your own way and pursue other quests, but you won't be able to complete this quest until you meet up with Preston again in your old neighborhood.