Hello!
The “West Bank Barrier/Wall” [also dubbed the “Apartheid Wall”] is a wall being constructed by Israel within the West Bank of Palestine. The wall is meant, according to Israel, to serve as an added layer of defense against Palestinians, to protect the Israeli people. The problem with that, however, is that while protecting the Israeli people, it has subjected Palestinians to an even more restrictive occupation.
The wall is being built mostly WITHIN the border of the West Bank, as opposed to being built along the border, or even on Israeli territory. The follow is a map created by ProCon.org, with the Apartheid Wall’s path displayed in red, and the border of the West Bank displayed in green:

As you can see, it weaves in and around Palestinian territory, essentially isolating the villages the Israeli government chooses to enclose within the wall.
The wall also serves to cut Palestinians from their land, often leaving farmers seperated from their crops, villages separated from their water supply, and as I mentioned, completely enclosing various communities within the wall, effectively serving as literal prison walls, forming an open-air prison.
This wall dwarfs the size and scale of the Berlin wall,

Keep in mind that the length is now projected to be 700 kilometers, rather than 650.
The wall has also led to a number of environmental issues on top of the already severely hindered agricultural ones, such as the case in Beit Hanina where the village was basically flooded by rainwater because the Wall restricted the flow of surface water, causing it to pile up and collect within the village.

The wall also cuts of tens of thousands of Palestinians from the rest of Palestine, trapping them on the Israeli side of the wall, while denying them entry into Israel, while at the same time implementing a crippling system of checkpoints that make entering into the West Bank such a hassel that many simply choose not to.
To get an idea of how large the wall is, here is a picture of me [standing at 6’1] next to a portion of the wall in Bethlehem:

As well as another photo showing how the wall weaves around Palestinian villages:

You see the alley the wall creates? That’s the road cars are supposed to drive on to get to where they need to.
Needless to say, the Apartheid Wall that Israel is constructing, although being built in the name of “defense”, is no more than another tool Israel is using to steal more Palestinian land, trap Palestinians, and cripple the Palestinian economy.
For more reading, you can check out the UNRWA Barrier Monitoring Unit, as well as the 2011 B’Tselem Article regarding The Wall