Logcat, is a simply data streaming from Android system, which describes whatever is happening just in time when u use the phone.
With a beneath tool, you can see and save that streaming into a file.
That file is then for us developers a very useful document to read errors and fix, we always use it for FC(ForceClose) or bootloops(phone in endless bootanimation)
Better is to use a computer, install last Samsung Drivers and download this Please login to see this link.
Once installed, head over to folder where is, and double click on MAF.exe, a command prompt will appear, type:
adb logcat > log.txt
and push enter
if all is ok(drivers installed, phone connected) you will see a cursor just blinking, perfect, recording is in action, wait about 30 seconds, maybe reproduce the bug on the phone more times...
Now push CTRL c to stop recording, the "file" will be saved in the same folder as where you click to launch above exe.
DONE, provide file to us when YOU FACE A FC OR BOOTLOOP we will for sure give you a Medal and fix the issue.