Feeling

It’s Normal to not feel much in the beginning. Also,you don’t need to clench,you really don’t have to contract very hard. You’ve also only just began to re-wire. We aren’t used to pleasure this way so the brain must build some new neural pathways for the pleasure feedback loop to run.

Do your best to relax,empty your thoughts,and have patience. Don’t expect prostate massage to be as direct and obvious as a punch in the face. Often it’s a feeling that just exists,small and subtle,in the background if you like,and with time,it amplifies.

Keep training,ask questions here and you’ll be grand soon enough.

It is indeed normal to not feel much at first. You can't go hunting for an orgasm. You have to wait patiently until it comes by itself.
No voluntary contractions or very light voluntary contractions are better than strong ones.

Welcome and congrats on your excellent decision to start your prostate journey. 

I recommend you read this thoroughly:

https://community.aneros.com/community/general-discussion/introductory-message-to-new-members/

There are many useful links within, and the best is to start with reading the entire Aneros wiki page. You will learn that it is a slow adventure, and sensations might take time to develope. Perhaps, weeks, months or even longer for some! Patience is the key, and  reading helps a lot!