It is very simple to invite Slack users to your DailyBot organization.
Add members form Organization Members window
Go to Organization Settings > Members and open the members management window.
From this window you can add/invite new members to the DailyBot organization.
Be aware that when you add members from this window, these members will join the organization but they won't be members of any team yet, you will require to add them to teams later.
Add members from within a team
Go to Organization Settings > Teams (tab) and then open the members window of one of the teams.
From within this window you can add/invite new Slack members to the DailyBot organization, they will join the org and will join this team automatically.