Boundary Conditions with Weak Form PDE's

Hello!

Quick question, when I make the weak form of my PDE, I end up with domain and surface integrals.

Do I input both types of integrals in the same spot? Are the surface integrals like using boundary conditions? If so, can I not put in the surface integrals and use the built in boundary conditions in comsol instead, like Periodic?

I'm attempting to solve a 2D transient diffusion problem.

Thank you for you help!