It's a good best practice to save your changes frequently to keep from losing work.
a) In Smartsheet, you save changes by clicking the Save button on the left toolbar.
When there are unsaved changes in the sheet, the Save button will be blue. Clicking the button when it's blue will turn it grey.
b) When the button becomes grey, you'll know that all those changes you've made to the sheet have been saved.
- The shortcut key for saving is Ctrl+S (Windows) or Cmd+S (Mac)
- To configure auto-save options, click Account > Personal Settings > Settings
- To save a sheet outside of Smartsheet, export it to a format of your choice (see how to export to excel)