i wear Studio Fix (powder foundation), and i dont know if i should wear concealer before or after application of my foundation, since my foundation is a powder (and generally concealer goes after foundation but before powder).

I would suggest after foundation (it tends to last longer.) is applied with a soft brush and blend upward toward the brow. Once you've made sure there is no line separating areas with foundation and areas without, you can lightly dust a colorless powder over entire face with a large brush. Let me know if you have any questions, I've been a Lic. for 5yrs to do (California Esthetician) Skincare/Make-up/waxing...