The highlight tool allows you to highlight and save text.

If you are not signed into Ebook Central, you will be prompted to sign in when using the highlight tool.

To highlight text, open the ebook in the reader:
Click the highlight icon and highlight the text.
Or
Select the text, and the highlighter options will automatically display. Select the highlight color. 
highlight text by selecting the text

To view highlighted text, go to your bookshelf. Ebooks with highlighted and annotated text will be saved to your bookshelf. Click “annotations” to review your highlights or annotations.
the link to annotations is under the ebook's bibliographic information and description

Or, click the star icon in the left side navigation of the reader.
review the highlighted text by clicking on the star in the left side navigation of the reader

To delete a highlight, click the star icon to view the highlighted text. Then, click the trash icon to the right of the text.
to delete or remove a highlight from the text, click the star icon on the left side navigation and then click the trash icon to the right of the highlighted text