Krawnix's lair is a pre generated small map that can be confusing to navigate but there are chests around so I suggest exploring. There are two spawn points one in the center and one before the boss itself.
Krawnix is not a hard boss if you stay calm... He has two attacks first he fires out a green plasma flame (or something like that) that homes in on you. it lasts for about 10 seconds so its pretty simple to just jump over and by the time it comes back around you it will disappear. The second attack is where he spits out two crawlers, as you can imagine this does not need mush explaining other that when you have crawlers below and plasma above this can be scary but again remember just stay calm and be smart.