unlocking the jaw

I am new here, and there is this emphasis on unlocking/relaxing the jaw.   I have no idea what that means.   And I cannot do these lip trills for the life of me.    I have tried umpteen times.   This has already become to frustrating to continue.   I must be defective or something.  

Straw singing is a great replacement for lip trills! Here's a lesson with other alternatives: https://www.youtube.com/watch?v=0wzbyyl1d-I. 

If you want to keep trying, here's an article on lip trills and a short lesson with extra tips as well. 

Here's a short lesson on jaw tension: https://www.youtube.com/watch?v=7TGV_6v-2UE&t=1s.

Hope these help!