Are you using the old SCID or SCIDvsPC?
Question About Scid

I think I'm using just regular SCID. Not SCIDvs.PC. What is the difference? Can you train openings in SCID vs. PC?

I just downloaded scid vs. pc and noticed some differences. First off there is no training opening button. Too bad. I don't think this feature works in the old scid. Hopefully the publisher will add training openings in the future. Secondly, scid vs. pc is better in the fact that you can add moves to the opening book known as book tuning. Thirdly, the layout is a bit different. There is no database switcher feature in scid vs pc.
I have a questions about scid vs pc. Can you merge/add moves from a pgn file into the book to add moves quicker?

I just downloaded scid vs. pc and noticed some differences. First off there is no training opening button. Too bad. I don't think this feature works in the old scid. Hopefully the publisher will add training openings in the future. Secondly, scid vs. pc is better in the fact that you can add moves to the opening book known as book tuning. Thirdly, the layout is a bit different. There is no database switcher feature in scid vs pc.
I have a questions about scid vs pc. Can you merge/add moves from a pgn file into the book to add moves quicker?
https://www.chess.com/blog/SamCopeland/tutorials---scid-for-the-chess-student
Not sure if the above is helpful or not.

You can create books, import books, or merge books together. See topics: book window, book tuning. Hope this helps!
http://scidvspc.sourceforge.net/doc/Index.htm
EDIT - BTW - This isn't such an old topic, seems very busy with helpful people: https://www.chess.com/forum/view/general/scid-vs-pc?lc=1#last_comment

Scid is nice for analysis, but I hate it's database functionality. I can't ever seem to just add a game of mine to its database and then query that database. I need chessbase for $350/year. But I just can't shell out that much without feeling worried about the quality of chessbase.

When you get that message, you have to tell SCID what type of training you want to use your db for.
You do this by clicking on Database->Maintenance->Maintenance Window.
The Maintenance window will open, and you have to click on the icon in the upper right side of the window. (this is the "right" the error message is asking you for.)
When you do, you will get a list of the ways you can use this database. If you want to train openings as white, then select "Openings for white". Click OK, then close the db maintenance window.
Now go to Play->Training->Openings. A little window should appear where you can set parameters; if you want to train White, select the "white" radio button.
Click "continue".
If you are using a large db, you will see SCID loading the moves, with progress indicated with a blue bar.
When it is finished, another box will appear with four bands of color in it, where you can set a few more parameters.
Now you can start training moves. If you make a move that is not in the db, an error box will appear.
Happy training!

Scid is nice for analysis, but I hate it's database functionality. I can't ever seem to just add a game of mine to its database and then query that database. I need chessbase for $350/year. But I just can't shell out that much without feeling worried about the quality of chessbase.
You have to create a databases to store games for manipulation and querying.. The clip base is just a temporary DB, kind of like a clipboard.
If you need help, please contact our Help and Support team.
If anybody can reply and tell me how to train openings that would be helpful. I get message saying: "open first a database with icon/type set to the right side". What does that mean?