StaffPad requires a device with active pen and touch. It's not the pen that enables pen-input on tablets, it's actually the screen technology itself, and it requires a special chip and sensor board for the devices to be able to pick up the signals emitted from the pen.
Having dedicated pen support is becoming more common for tablets and laptops, but if you own a device and aren't sure if it supports pen, you can do a simple check:
On Windows 10, type "pen" into Cortana/Search in the Windows Taskbar. You'll see an entry for "View Pen and Touch Info". Under the "Pen and Touch" setting, if you see "Full Windows touch support with 10 touch points with pen" then your device is compatible. If it doesn't specifically mention pen, then your device isn't compatible.
If it mentions pen support, but you don't have a pen for your device, as is the case with some HP, Dell or Asus devices, then it's worth checking with the manufacturer to see if they sell a pen direct.
You can also Google your device make and model number, followed with "pen" and if it mentions Wacom, N-Trig or Synaptics in the specs/features, you'll be good to go.