A Variation is an alternative sequence of moves at a particular point in a game. They can contain comments and recursive subvariations.
The buttons are used to exit, enter and add variations respectively. And in the Edit Menu, and PGN context menu, are further useful commands.
If you want to enter a variation without being asked for a confirmation, use the middle mouse button of the mouse to enter the move.
Scid vs. PC has clickable Variation Arrows (enabled via Options / Moves / Show Variation Arrows). But for this feature to work, the Variations Window (Options / Moves / Show Variation Window) must first be disabled.
This feature (in the Edit Menu) will try to add the currently selected text as a variation. It is not very sophisticated; but very useful when adding a single line of MulitPV analysis from a paused engine.
Please see below in regards to adding null moves.
When a move has variations they are shown in the game information area. You can click on a variation to enter it, or press "v", whence the Variation Window will pop up. Setting Options-> Moves-> ShowVariationWindow will automatically show this window when a variation is found.
In the variation window one can select a variation with the up/down keys and then hitting enter, or pressing 0, 1, 2 etc for each variation. Additionally, 'vv' will enter the first var.
To leave a variation, use "z" or up-arrow.
Null moves are used to skip a move by one side. This is of course illegal, but is a well known idea, and useful for analyzing your opponent's immediate threats.
Null moves are displayed as "--" and can be made by typing this string, or by using the mouse to make a King x King capture. They are not a part of the PGN Standard, so when exporting games to PGN, Scid provides (among other options) one to convert null moves to comments - for compatibility with other software.
Some other programs use
One final issue arises with Engine Analysis. If you have null move at then end of a game or variation , the analysis window will not successfully add a variation to it. Instead, one should first add a single move, then variations may be added. This note also applies to the Paste Variation feature.