Samsung Galaxy S6 Edge
TWRP
Download Odin then TWRP 3.3.
TWRP:
Restart the device. Before the device begins to boot, hit Home + Power + Vol-Down. You will see the download screen. Confirm by hitting Vol-Up.
Start Odin3. Click on AP and select the TWRP .img.tar file. Ensure that Auto Reboot is disabled. Ensure that F. Reset Time is enabled. Click on Start. Once the file has been downloaded to the device, reset the device. Before it boots, hit Home + Power + Vol-Up. You should see TWRP.
Lineage OS 16
Download NexusOS 9. Whilst in TWRP, load the .zip file into the device. Wipe system and data. Then install the .zip file.
Download GApps
Load and install the .zip file.
See Also
Guide
NexusOS 9
Root Without PC