Can someone please explain in Breaking Bad the part where Jesse makes the box?

Ah yes, the wooden box was addressed when Jesse was in rehab earlier in the series. He told a story about when he made a wooden box for his mom, but he lied and said he traded that wooden box for an ounce of weed.

Breaking Bad Jesse Wooden Box

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Jesse described making it to his NA group in episode 9 or season 3 (Kafkaesque).

He said he took a shop class where they were supposed to make a box:

"I took this vo-tech class in high school, woodworking. I took a lot of vo-tech classes, because it was just big jerk-off, but this one time I had this teacher by the name of... Mr... Mr. Pike. I guess he was like a Marine or something before he got old. He was hard hearing. My project for his class was to make this wooden box. You know, like a small, just like a... like a box, you know, to put stuff in. So I wanted to get the thing done as fast as possible. I figured I could cut classes for the rest of the semester and he couldn't flunk me as long as I, you know, made the thing. So I finished it in a couple days. And it looked pretty lame, but it worked. You know, for putting in or whatnot. So when I showed it to Mr. Pike for my grade, he looked at it and said: "Is that the best you can do?" At first I thought to myself "Hell yeah, *****. Now give me a D and shut up so I can go blaze one with my boys." I don't know. Maybe it was the way he said it, but... it was like he wasn't exactly saying it sucked. He was just asking me honestly, "Is that all you got?" And for some reason, I thought to myself: "Yeah, man, I can do better." So I started from scratch. I made another, then another. And by the end of the semester, by like box number five, I had built this thing. You should have seen it. It was insane. I mean, I built it out of Peruvian walnut with inlaid zebrawood. It was fitted with pegas, no screws. I sanded it for days, until it was smooth as glass. Then I rubbed all the wood with tung oil so it was rich and dark. It even smelled good. You know, you put nose in it and breathed in, it was... it was perfect. "

The leader asked him what happened to the box. Jesse said he gave it to his Mom...the leader saw that as an opportunity to help Jesse find some direction in his life and suggested that he go back to school to be a carpenter. Jesse then revealed that he didn't give the box to his mom...that he traded it for an ounce of weed.

It was a flashback scene.

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it was a flash back and I think that is how Jesse was coping with being a prisoner there