Joe works as a blacksmith, and his forge is adjoined to his house. He is married to Pip’s sister, and they lead a simple life. Joe’s good nature is first shown when he protects Pip from getting flogged by Pip's sister.
When Pip is in London training to be a gentleman, Joe pays him a visit. Although Pip looks down on Joe and makes the visit awkward and uncomfortable, Joe does not reprimand Pip but instead asks him to visit him at the forge, where the environment is cordial and welcoming.
After Magwitch’s death, Pip falls ill and goes in and out of consciousness. Joe nurses him back to health and also pays Pip’s debts. Joe helps Pip recover from the debts he has accrued due to his lavish spending. Despite Pip’s negative attitude toward Joe, the blacksmith helps him in his moment of need.
Oh, Joe, you break my heart! Look angry at me, Joe. Strike me, Joe. Tell me of my ingratitude. Don’t be so good to me!
In Chapter VII, Pip has been attending Mr. Wopsle's great-aunt's school and learning his alphabet and how to write. One night he exerts great effort in writing a letter to Joe; when he gives this letter to Joe, Pip realizes that Joe is illiterate. So, Pip asks Joe why he never attended school, and Joe explains that he went to work at an early age. Then, Joe confides in Pip that Mrs. Joe would not like it if her were to put on airs and be "a scholar."
Young as I was, I believe that i dated a new admiration of Joe from that night. We were equals afterward....I had a new sensation of feeling conscious that I was looking up to Joe in my heart.
There are some good descriptions of Joe in chapter 2. For example, Joe is described in the beginning of the chapter this way.
He was a mild, good-natured, sweet-tempered, easy-going, foolish, dear fellow—a sort of Hercules in strength, and also in weakness.
Joe is strong and weak at the same time. He is strong physically, but he also does not stand up to his wife. He is weak-willed.