Welcome! 
First things first: you have to have devices which can be recognized by your smartthings account. Some of these will be devices that communicate directly to the SmartThings hub, others will use a “cloud to cloud” integration where your account for the device communicates via the Internet with your SmartThings account.
It often comes down to the exact brand and model of a device. For example, some of the Schlage locks, in particular the Z wave and zigbee models, are recognized by your SmartThings account. But the Home kit and Bluetooth models from Schlage are not.
The D-Link motion sensor is not recognized by the SmartThings account, but it does have its own IFTTT channel, so you may be able to use that for some simple automations.
The Leviton Wi-Fi switch should be recognized by your SmartThings account, so that one is easy.
While you’re checking the model numbers, I suggest you take a look at the following intro FAQ. I think it will help answer some of your basic questions. (This is a clickable link)
Also, before we go any further, are you using an iOS phone or an android phone?