Every import you've run is listed underneath the upload area on the Imports page, newest first. This is where you follow one through and where you come back for the results afterwards.
Each row shows the import's ID with the name of the uploaded file underneath, the Type, the Admin who ran it, its State, its Results, and when it was Created.
State is the short version of what happened:
Requested — queued, nothing has been applied yet
Processing — running right now
Finished — done
Errored — it didn't get through
Reverting / Reverted — being rolled back, or already rolled back
Cancelled — stopped before it finished
Results counts the rows: how many succeeded, how many were skipped, and how many failed. While an import is still moving, this column says Queued or Running… instead.
Click View in the Actions menu to open the import. While it's running, that page keeps itself up to date — it shows how many rows have been processed so far and the running split of successes, skips and failures. You don't need to refresh it.
When it finishes, the page shows the totals and a Download Results (CSV) button. The table underneath lists the last 100 rows with the message recorded for each one; the download has every row.
The Actions menu also offers:
Download Results — the same results CSV, without opening the import
Run Again — re-queues an import that was queued, errored or cancelled, using the file you already uploaded. It doesn't appear on an import that finished, because running that again would apply the whole file a second time. It also needs the original file to still be stored with the import; if it isn't, upload the file as a new import instead.
Remove from List — hides the row. This does not undo anything the import did.
You can also download the file that was imported: click the filename under the ID in the list, or use Download Source CSV on the import's own page.