[Galaxy S6 General] avidichard:
Installing TWRP with ODIN

A simple Google search makes it easy to find but, having a thread like this one , I believe that your questions are relevant. So...

Question #1 (getting TWRP on your phone): 2 links to start with ODIN to make the flash and TWRP, the thing you need to install:

ODIN (remove spaces in the following link): ww w.droid views.com/download-odin-tool-for-samsung-galaxy-devices-all-versions/

TWRP: https://twrp.me/samsung/samsunggalaxys6.html

Follow the instructions on the ODIN website. ODIN is used to flash your phone to have TWRP installed. Also note that this process is pretty critical as it can brick your phone so be carefull and follow the instruction properly. I have flashed TWRP a few times without any problems on my side.

Question #2 (Installing a custom kernel):

I have not tried this and did not adventure myself into installing any such thing. I tend to stick with original stuff to make sure to not brick my phone. AND seeing that many custom ROMS for Pie are not out yet and also seeing the battery problem with OREO, this simply means that noone has ever found anything stable yet for this device. I don't believe that installing another kernel may make things work better. But this is just an opinion and since I did not try any custom kernel, I don't believe to have the best answer for you concerning this.

Question #3 (Camera issues with custom ROM):

Samsung Galaxy S6 is made to work with Marshmallow abreviated as MM in certain threads and posts. So anything after MM is a risk, stable or not. I had XtreStoLite for many years and I had absolutely no problems until some apps just said that MM was not supported anymore. That's pretty much the only reason I decided to install something new. I also noticed that Nougat is still very popular but have not found any Nougat ROMS that were not too heavy or simply unavailable for my Canadian phone. But, if you install any MM ROMS, your are mostly not going to have any problems. You could try OREO roms and fall in luck and find someone that figured out how to elliminate the battery issue but in my case, I tend to stick myself to the latest ROMS and live temporarly with my problems until an update fixes it as I don't have too much stuff on my phone that makes me take the reinstallation as a waste of time. I can install over 15 custom ROMS in one day while only 3 or 4 Windows during the same period, I believe that trial and error in this case is worth it. There are few stable builds that correspond to my criterias which are very few custom apps and lightweight that are less than 650 mb ROMS. Most roms go over 2 Gb while som maintain between 1.2 to 1.7 gb which I find pretty huge to my opinion seeing I can get a fully working rom for 550 mb.

I hope this helps a bit. I'm not one of those geeky people with all the technological knowledge to explain or understand the nuances of kernels and roms. I'm not a developper nor a ROM creator myself so just following the installation processes proposed makes me a simple user. I applaud those creating custom kernels and roms from scratch with nothing but their knowledge without any installation instructions until they figure out by themselves how to explain their procedures, these people are the real fun guys or girls that make us use our phone to their outmost potential without any controls giving us the freedom to use the full unlimited functionalities of our android phones.