There are two ways your SigFeed can be updated; Scheduled Updates and Ping Updates. Scheduled Updates updates your SigFeed every six hours. Scheduled Updates is easier to set-up and configure. Ping Updates can update your SigFeed as soon as you post a new entry on your blog, but it requires a little bit of configuration and/or interaction on your part to make it work. This page describes Scheduled Updates.
New SigFeeds default to using Scheduled Updates when they are created. If you want to confirm that your SigFeed is using Scheduled Updates, or switch it back to using Scheduled Updates after you've switched it to using Ping Updates, go to the Your SigFeeds page. Select "Modify Settings" from the Action menu of the relevant SigFeed. In the "Update type" section of the next page, select the "Scheduled Updates" radio button. Then click the "Modify Settings" button at the bottom.
Scheduled Updating is done in "blocks." New SigFeeds are assigned a block when they are created, and each block has certain times of day which they are updated. When it's time, SigFeeder checks the RSS feed for every SigFeed in that block for updates. If it finds that a feed has been updated, it updates the SigFeed accordingly.
And that's all you need to know to use Scheduled Updates. I told you it'd be easy!