Hey everyone, i’m new here, it’s my first post, so please be forgiving just in case

My goal is to install custom ROM, so first I unlocked bootloader via Flashtool. It worked well.
Then I rooted the phone via KingRoot, it also worked well.
The next step I wanted to do was install the custom recovery (TWRP), so I installed TWRP Manager app and it failed:(
I installed it via Terminal Emulator app following the instructions on the twrp website and it kind of worked, but I can’t get into TWRP…
Turning of the phone, holding the volume down button doesn’t work. It’s just booting the system. How to fix it? Maybe i’m booting to the recovery wrong?
Help me please, thanks in advance. And sorry for my bad english