You can assign labels (tags) to the puzzles so you can locate them later by choosing the view Labels in the gallery and then the label you are looking for.
To label a puzzle right click on its thumbnail. It will appear the window where you can enter the different labels you want to assign to a puzzle.
You can type any name in each line. If the puzzle had already labels assigned you will see them too in the list.
At the right of each label you can see a small cross to remove that label from the puzzle easily.
If a label you type didn't exist previously it will have "New" at the right so you are aware that you are creating a new label. (This may be useful to avoid creating more than one label with the same meaning. For example if you labeled some puzzles with "Landscape" previously, if you are entering "Scenery" and see the New next to it it may alert you that you are entering a label you didn't intend)
Labeling multiple puzzles.
If you select more than one puzzle in the gallery and then choose to label them (right clicking the mouse on some of the selected puzzles and choosing Label puzzles), there are some particularities:
If there are certain labels in some of the puzzles but not in all, these can not be removed. (They will be displayed as a note in the labeling window)
Any new label you enter will be applied to all the selected puzzles
If there were labels common to all the puzzles, these can also be removed for all in a single shot.