How To Install A Custom Rom

The best way to flash custom rom is using twrp on samsung device but process is same for oneplus 3.
Step 1. How to get TWRP
Step 2. How to get custom rom
Step 3. Procedure for flashing
Watch Full Tutorial HERE
Flashing TWRP post is written by me
To get custom rom just search google and select all modes you love but from official websites like xda developer
Procedure for Flashing
First in TWRP go to wipe>advanced wipe>system data cache>
Then flash rom