You can export any graph or table that has an "Export" button on the top right.

In some cases (like in Keywords Explorer), the option to Export can be found in the 3 dot menu on the right:

Many graphs provide the option to export the data. For example, you can export this Performance graph in Site Explorer Overview:

Once the "Export" button is clicked, a CSV file will start downloading in your browser's default downloads file. Here is an example of exporting the chart from the Top Pages report:

The lower table in Site Explorer > Top Pages report is an example of a table that you can export:

Once the "Export" button is clicked, a window will pop up giving you options to choose the Number of rows and Format of export:

The number of rows you export count against your subscription's Export rows per month limit. Use the "Custom" option to set a specific number of rows you wish to export. The max amount of rows you can export depends on your subscription plan:

Then, choose the format that best matches the spreadsheet application you plan to use.

Once you click on the orange Export button, a CSV file will start downloading in your browser's default downloads file.

This is a feature currently available in Keywords Explorer, but will soon be rolled out for other reports as well. In Keywords Explorer you have the option of exporting the report to Google sheets. For this option to work, you need to first Link your Google Account:

Please note that this is still an export, and your Export rows per month limit will be consumed the same way as an export to CSV will.