Default Rooted Xperia Z

Hi guys. Been reading for a long time but it's still all so confusing. Kernel this, twrp that etc

I have a rooted Xperia Z. I figured out that the bootloader is locked.

Without access to a PC, how can I get a custom rom on my Xperia?

For some reason I cannot get into recovery mode via hold power then Vol up wait for 3 vibrates method.

I made a nandroid back up already.

What do I do now? In basic dumbass terms please. Lmao

Sent from my Xperia Z using xda app-developers app