Need help with twrp

My device is on miui v6.6.2.0 global stable.I wanted to root it,so gave twrp recovery a go.I installed & booted into twrp,but I am unable to reach the next step(install the 'super su' zip file located on the phone storage) because the phone storage is not listed there.As a corrective measure I wiped the 'dalvik cache',but after that, the play store app is missing, & I don't know how to recover it. If anyone could help, it would be great.
Also I would like to know if there is a way to revert back to the stock recovery from the twrp.