Torn up inside over iperf3

Hey r/networking!

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This is my understanding of iperf3:

The client (iperf3 -c 10.0.0.5) is uploading to the server (iperf3 -s) and the result of using those options with the command will show the upload speed of the client.

If the client uses the -R option (iperf3 -c 10.0.0.5 -R) the download speed will be tested from the server.

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Am I correct about how it works? I can't believe how confused I am over this. Gotten lots of contradicting answers from people.