We have 2 smart TVs that we use for streaming, we do not have cable or dish, just internet, and are wanting to get local channels. Can I just get an antenna on Amazon and plug it into the TV, or do I need a converter box as well? I am a complete idiot when it comes to this tech stuff so any help would be appreciated!

Just an antenna.  Smart TVs won't have any problem like needing a separate box to convert to digital.  
   

I am not an expert, just user. Depends on your location, type of antenna, and terrain between you and the station broadcasters.

I have several types of antennas. They all seem to work about the same. I buy the ones that have the longest range in miles. You position the antenna at a high point in the room near the TV, hook it up to your TV coax input, select the TV or antenna input on your TV menu, do a scan for channels. It will run through all the channels digital and analog and your done.

Sometimes the stations change, so you may need to rescan after a few months.

Thanks for the help guys. I went ahead and ordered one to try out.

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https://www.antennaweb.org/

the site gives you strength and bearing info,
10 degrees off axis is not going to sync

with digital broadcast you either get the channel or you do not

there is no watching a marginal signal like with analog broadcast

When I went to antenna I bought a DVR that functions as the tuner and records shows.
It was a one time cost and no other fee, unfortunately they no longer sell it and I only see ones with a monthy fee for sale now.
My TV is not smart, I use an old Xbox for streaming services.

https://www.channelmaster.com/pages/ota-dvr

I've been using an OTA Indoor Antenna for a few years now.
Imagine watching commercials For Free!