After you've created your schedule, you'll want to get started, of course! To help orientate you on the site, please refer to the screen grab below;
To add your first schedule task (which in your organisation you might call an activity or just 'task'), select the blue floating action button in the lower right hand corner.
You can select schedule task or milestone - selecting either is fine, you can change your selection any time before saving your new schedule task.
When you select, a modal will appear where you can populate the details of your schedule task. Not all fields are compulsory, so just add the information you need and have a go at saving it.