Take end of rope and make one full wrap around post.
Make a second full wrap around post, leaving a gap between the first wrap and the post.
Bring end of rope fully around under the 2 wraps.
Then push it up through the gap between the post and the rope.
Pull end of rope in downward direction to start tightening.
Now bring the end back and under itself, then use a reverse half hitch to lock it all together.