The only way to vote

[cessna152towser]

There are 73 "constituencies" in Scotland. A person living in, say the constituency of Aberdeen Central, would vote vote for the one person on a slate they would like to represent them in the Scottish Parliment. This is a "first past the post" system, with the candidate with the most votes winning outright.

Now, this person in Aberdeen Central is also part of a larger "region", of which there are eight in Scotland. Aberdeen Central is part of the North East Scotland region. So, the voter would also mark their preferences for the various parties running. They don't vote for an individual here, right? In the end, each constituency sees the top vote getter going to the Scottish Parliment, and each region also has a "regional representative" go to the same Parliment?

But if this was a national election, the voter would be ticking off a check next to a candidate who would represent a different constituency altogether, as the Westminster elections have different constituencies than the "local" elections?

Almost correct. The only proviso I would add is that the winning party under the party list system isn't necessarily the party which gets the most votes. The party list system is intended to give preference to parties whose individual candidates were runners up to ensure that strongly represented minorities also obtain representation as well as the first past the post constituency winners. There is a complex formula for weighting the party list votes which penalises parties who have already won constituency seats.