A scheduled task — a cron job — runs something on your site at a set time without anyone being there.
Where
My Hosting → Cron Jobs.
Do you need one?
Usually not. WordPress runs its own scheduled work — publishing posts you have queued, checking for updates, sending the emails plugins send — without anything being set up here.
You would add one if a plugin's instructions specifically ask for it, if WordPress's own scheduling is unreliable on a quiet site, or if you have something custom to run.
If a plugin asks you to add one
Follow its instructions exactly. If the wording is unclear, send us what the plugin says and we will set it up correctly — a mistyped schedule either never runs or runs far more often than you intended.
The file manager
My Hosting → File Manager sits alongside this and lets you browse your files in the browser, without an SFTP client. The same warning applies: take a backup before editing anything.