Look at your GPU.
It should have two 6-pins plugs (or 6-pins + 8-pins) to power it.
Look at your PSU, what kind of remaining cables (from your previous GPU or unplugged) do you have?
If you have 6-pins / 8-pins connectors, just plug them directly into your GPU.
The adapters in your picture are Molex to 6-pins.
Molex is simply another type of connector that is usually used to power case fans or front panel.
You are not compelled to use them, it is simply an alternate solution if you only have Molex connectors left.