If you haven't already, click A/B Tests above and then click "New A/B Test". You'll give the test a name, save it, and then see a code snippet that looks like this:

<ABTest
  abTestId="abt_e8ed892b652c835bb785988aa4464fbf"
  variantAId="abv_323823556cd3a6453f8e54c18d65f41c"
  variantBId="abv_9d407d4c470ced71f53677ec89732c1c"
>
  **place two child elements here**
</ABTest>

Copy the code generated for your test and paste it into your project and place two children inside the ABTest component.