I needed to move something so I copied it and pasted it to its new location and now where I have pasted it there is a selection pane that will not go away.
I’ve tried to move the pane and tried the “Select All” function (Ctrl + A) to no avail.
When you paste something into GIMP, it becomes a floating selection. That’s a sort of a temporary pseudo-layer that contains the pasted content and allows you to move it around (and edit it in other ways) before actually merging it into the target image. However, having a floating selection active also prevents you from making any edits to anything but the floating selection.
To see whether you have a floating selection, take a look at the Layers dialog, where it shows up as a special layer. Also, when your mouse pointer is outside the floating selection (but inside the image window), an anchor symbol is shown next to it.
There are two main ways to get rid of a floating selection:
You can anchor it to the current layer with the Layer → Anchor Layer command (Ctrl+H), or by clicking the anchor icon in the Layers dialog, or simply by clicking anywhere in the image outside the floating selection. This merges the floating selection into the current layer, overwriting whatever else may have been under the selection.
Alternatively, you can convert the floating selection into a new layer by using the Layer → New Layer command (or the New Layer button in the Layers dialog) while the floating selection is active. This turns the floating selection into an actual layer that you can edit at your leisure.