I know this is REALLY basic, but I've got a new MacBook and external monitor, and I can't get my mouse or trackpad to jump on to the external monitor. It's got to be obvious, but I can't find it in the manual or in help, and that's frustrating. The displays are linked, side by side, but the mouse doesn't seem to know it. I'd be grateful for any help.
(Migration Assistant appears to be a big dud as well, but that's another story.)
(Migration Assistant appears to be a big dud as well, but that's another story.)