Make sure you have entered sufficient information for everybody included (users can also add this information themselves on the User page)

Add the users whose signatures you wish to set daily into Subscription by ticking the checkbox next to their name in Users & Set-up and clicking on Activate the subscription mode below the list of users. You can see the number of used/available subscription seats in Subscription settings.

The users in Subscription now have a purple box, while the ones in Credit mode an orange one.
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Next signature set-up will occur at a time that you can see under the section Time of daily set-up in Subscription settings. You can change the time of the next set-up after this one there, too.

You don't have to wait for the scheduled set-up, you can always set the signatures manually. The details are described in a dedicated article.