How do I put a PGN file into Scid for analysis?

This partially depends on what you have now. Do you have a .pgn file saved in a folder, or do you have a pgn you have copied to your clipboard?

If you have a pgn file already, you can import it by clicing Tools, Then selecting Import File of PGN games.

Or click [File] from the Menu Bar and select [Open] from the drop down menu. Then navigate to the folder and click on the file.

Or click the "Open" Icon on the menu bar and navigate..., etc

Or if your default is SCID then just click on the .pgn in the folder and SCID will open.

If you have a notepad version of the pgn such as you usually get from a database game explorer, you can ctrl-a then ctrl-c to copy it to the clipboard.

Then click [Game] on the menu bar and select [New Game]

Then click [Edit] on the Menu Bar and select [Paste PGN]

A small window will open.

Right click in the blank space and select [Paste]

Then click [Import]