Weak form PDE Boundary Conditions-Weak Term Edit Field

Hi,
I am trying to solve equation that has a weak form:

-ux*test(ux)+a*ux*test(u)

My boundary conditions are:

ux(-L,t) -a*u( -L,t)=0 and same for the other end x=0

I am very new to the Comsol and I am confused on whether I should edit the "weak term" edit field as, ux*test(u) with
" constr" edit field as, -ux+a*u
or leave the weak term edit field as zero and just edit the constraint field. Because it alters the results.

Is it necessary to edit the weak term edit field?

Thanks in advance.

Best regards,
Ozgur Taner