Tunisian Simple Stitch is worked under the vertical bars which you created in your foundation row.
The very first one does not count as this is from the loop which you have left on your hook at the end of each reverse pass.
I am using a different colour yarn to highlight the stitch placement.
Insert your hook under bar 1.
Yoh and pull a loop through.
Repeat this to the end of the row making sure not to forget the very last stitch.
You should now have 16 loops on your hook.
Without turning, work a normal closing.
Try a few more rows for practice.