A backup is a full copy of the site: the database and wp-content — themes, plugins and uploads. Caches, other plugins' backup folders and temporary directories are skipped, because restoring them helps nobody.

Copies are held off-site in cloud storage, not on the site's own disk.

Taking one now

The site's Backups tab has Backup now. It runs in the background; the site stays online. Large sites take longer, and the progress is visible while it runs.

On a schedule

Schedules are per site: pick a frequency and a time. Weekly schedules also pick a weekday. Backups run against the site's own clock.

Retention decides how many are kept before the oldest is removed. Deleting a site removes its stored files as well — that is the one action that cannot be undone.

Restoring

From the same tab, choose a backup and press restore. What happens then:

The site goes into maintenance mode, so visitors see a holding page rather than a half-restored site.
The database is restored, then the files.
Caches are cleared — page caches, object cache, transients and OPcache.
Maintenance mode is lifted, including if something failed along the way.

A restore replaces the site's current content. If you are unsure, take a fresh backup first: it costs minutes and buys a way back.

When a backup fails

The failure reason is shown on the Backups tab rather than kept in a log you have to find. The common ones are disk space on the site, a PHP time or memory limit, and an unreachable site. Failures also raise a notification if you have that type enabled.