Fallout 4/When Freedom Calls

When Freedom Calls is the first of the Minutemen missions. You are directed to this quest if you speak with Codsworth when you return to Sanctuary, making it an early game quest.

It is possible to skip this mission, although it may become required depending on the results of other quests.

Red Rocket Truck Stop
If you approach the city from Sanctuary, you will likely see the Red Rocket Truck Stop. Here, you can encounter a dog, which you can recruit as a companion.

Concord
Concors itself is mostly empty, but at the Museum of Freedom, there is a current firefight between raiders and the minutemen. You can easily kill the bandits with a firearm. When they're cleared, Preson will shout at you from the balcony, telling you to pick up the laser musket, and enter to finish off the remaining bandits.

When you enter, you can either pick the advanced lock to the next room, or take the side rooms. You will need to defeat the various raiders in the lobby - in the early game, they're likely equipped with only light pistols and no armor, and are easily slain. You can reach the top floor by taking the halls on the left, where you will encounter a few distracted raiders.

When the lobby is cleared out, Preston will open the door and brief you on what else needs to be done. There is a fusion core in the museum's basement (accessed from the collapsed lobby floor), unlockable by a novice lockpicking or hacking. Take the core, and head to the roof.

On the roof, you can put the core into the power armor, and use the power armor to retrieve the minigun. Engage the remaining raiders outside. During the mop-up, a deathclaw will dig out of the ground and attack. This deathclaw is dangerous at higher difficulty levels, but can easily be evaded by hiding in one of the buildings (such as the one facing the Museum of Freedom).

After the deathclaw and raiders are killed, re-enter the museum. After a short discussion, Preston will bring his group to Sanctuary. TO complete the quest, head to Sanctuary yourself and speak with Preston. He will also immediatly provide the first side quest, "The First Step".