[G2 Q&A, Help & Troubleshooting] MilanStojkovic:
1. You won't if you do everything right. Titanium backup does the job, + most of it is already backed up to the play store / your Google account. You need to do your research more about: 1. Rooting the phone 2. Installing custom recovery and updating it 3. And eventually fflashing the rom you want with with all the prerequisite for it (the right baseband, bootloader etc. For your phone model)

2. Pretty much something like that, but there are some differences in later steps depending on the Rom you want.

3. Start with root and custom recovery. It's better for you to dig a bit about this info on your own and ask in specific threads. There is everything you need to know on this forum, and the more you read, the more you will understand about how things work. You are off on a good start, just be patient, ask before you do anything, follow the model specific instructions and ALWAYS BACKUP ;)

---------- Post added at 09:02 PM ---------- Previous post was at 08:50 PM ----------

Going back to stock kernel was impossible for me (there is probably some step I missed in flashing the stock back the right way after using dorimanx). But I couldn't even boot the phone. I am not sure what you can do if you don't have a full rom backup. As for the apps, use titanium backup always before flashing something new, or reflashing nandroid. It will ensure that you have all of your app data stored.

Is it a specific app you are having problems with, or in general?

If you are having problems and you wanna run stock kernel again, I suggest clean flash the Rom with it's native kernel. That will ensure you won't be getting any problems.

---------- Post added at 09:05 PM ---------- Previous post was at 09:02 PM ----------

It's like right on top of the 802 thread

http://xdaforums.com/lg-g2/development-d802/rom-stock-30d-flashable-zip-t3070383

---------- Post added at 09:14 PM ---------- Previous post was at 09:05 PM ----------

Haven't seen anything about formating, I wouldn't advise that unless you don't wanna loose all of your data. Try this one, works fine, and it's the latest.

http://xdaforums.com/lg-g2/development/twrp-twrp-2-8-0-0-kernel-f2fs-tools-t2898705

---------- Post added at 09:24 PM ---------- Previous post was at 09:14 PM ----------

Did you install lollipop bootstack from xdabbeb's thread? You need kitkat bootloader that's a part of it to run cloudy. If you are coming from blisspop (and that one has jb bootloader) you might have missed the step. Name the exact steps you did after blisspop

---------- Post added at 09:35 PM ---------- Previous post was at 09:24 PM ----------

Quoting xdabbeb for VS980. Should be the same for the other variants besides numbers, those are different.

"Our devices have a number of partitions that all work together to give us a functioning smartphone. Every time LG releases a new firmware there are certain partitions that get updated (aboot, dbi, laf, modem, rpm, sbl1, tz). This subset of partitions was given the arbitrary label "bootstack" at one point and the term stuck. They have been grouped together here in flashable zips along with a custom recovery and are referenced by their corresponding official LG version code (i.e. 12b, 26a, etc).

NOTE: Though the "modem" and "aboot" (bootloader) partitions are included, these terms are NOT synonymous with bootstack."

Kernel is not a part of the bootstack