I'm not sure where you're looking. SSL should be installed on your server when the server is built.
You should probably set your system to use the
Advanced skin supplied with DirectAdmin; that's probably the one most used, and which gets the most support.
From the DirectAdmin control panel admin level you can either click on
Reseller Level or you can click directly on
User Level.
Most of us work from the Reseller Level to create our own users, and create additional resellers from the Admin Level to create additional resellers for our clients who want to be resellers.
From the Admin level, the default reseller and user both already have SSL enabled.
From the Reseller level, before you can create Users you need to create packages. From the Admin level, before you can create additionl resellers you need to create packages.
It's when creating those packages that either enable or not enable SSL.
DirectAdmin documentation:
Site Helper for Administrators
Site Helper for Resellers
Site Helper for Users
Jeff