Bookmarks are incredibly valuable resources saving you time but also reducing the learning curve as you get started.
Bookmarking a chart you like means you will not have to rebuild it yourself. Bookmark a chart in search results or in a dashboard where you see the bookmark icon:
In the Dataset Viewer, you can bookmark both the dataset as a whole and a particular time series from this dataset. When some visualization is shown clicking a bookmark icon will add both a dataset and a visualization to your bookmarks. When you bookmark a table, it is added as time series and can be found in the tab "Data" of the bookmarks.
In Data Insights, you can bookmark both the dashboard as a whole as well as a separate gadget.
Once you bookmarked a chart, you can instantly add it to a dashboard or presentation you build.
Or, go to your bookmarks (bookmark icon is in the top banner), and select the charts you want to use to build a dashboard or presentation in a single click.