The first mention of the Nashua branch was in the episode "Local Ad" when Michael Scott is shown the Nashua branch's local commercial. The branch makes its first appearance in "Lecture Circuit Part 2" as one of the branches Michael and Pam Beesly make a presentation at.
The branch is also used as part of the plot of "Employee Transfer," where Holly Flax and Michael take a "road trip" after the CEO transfers Holly back to her old branch because of her relationship with Michael. Holly moves to Nashua during in the episode.
In one of the deleted scenes of "Branch Wars," Michael lists a specific characteristic of each branch, explaining that Nashua has "no parking." Pam also mentions that "the branch is only accessible though cross country skiing" meaning that the branch is in a rural area.
We know very little about the staff members of the Nashua branch other than Holly. In "Lecture Circuit Part 2", Pam makes up names for a few: "Blazer," "Freckles," "Penguin," and "K.D. Lang." The branch's regional manager can also be seen fairly clearly in the local commercial from "Local Ad," but remains unidentified.
In the episode "Survivor Man," Toby Flenderson mentions that a man named Mark Chisholm attended Ryan Howard's wilderness retreat, indicating that Chisholm is a regional manager. It is possible that he is the regional manager of the Nashua branch, though he could just as well be the regional manager for Rochester, Akron, Camden, or Yonkers.
Nashua Branch may have hired the first female HR worker of Dunder Miflin as in the episode The Dundees, Dwight mentions there not being any female HR workers for the company.