Hello RJean,
If the only cable you have is an HDMI cable you are missing your power cable / AC adapter as illustrated here in your manual.
Regarding which antenna to use, any run-of-the-mill HD antenna will suffice, you can click here for a recommendation from Amazon.
The HD antenna requires its own power and is connected to the TV via the Coaxial connection on the back. How to connect to the tv is illustrated in Figure A on the manual I shared above.
If you are indeed missing your AC adapter for your tv, you can get a replacement here.