I have been using Kodi to manage personal media for quite some time now but never really had any need for Kodi's built in capability to stream live tv channels. However, recently I did have a chance to test out a .m3u list.
Going by the online tutorials installing and setting up the Simple IPTV Addon was the way to go and was as easy as navigating to addons and installing the addon. Plain and simple. Unfortunately, it wasn't as easy as portrayed, I wasn't able to find the addon in Kodi's official repository.
Fix was rather easy, the addon availability depends on a linux package. In my case, I have a dedicated Ubuntu 16.04 installation running Kodi attached to TV. Stumbling across Kodi's Ubuntu PVR add-ons wiki I ended up installing IPTV Simple Client package by executing the following command,
sudo apt-get install kodi-pvr-iptvsimple
Restart Kodi after installing the package and you should be able to see Simple IPTV Addon listed under PVR Clients.
There's a bunch of other packages (for different addons) that might be of interest to you other than IPTV Simple Client.