Nasus is a late game offtank that becomes even more powerful if you farm correctly.

In a fight you want to start off by placing E between you and your opponent if melee or on them with the back of it towards there turret if ranged. if melee and you have full mana use wither this will make them take more damage before reaching you and if your Q is powerful enough slow them while there running away.you want to use Q whenever available this is especially important against turrets this massively helps finish turrets.

When farming its relatively simple. just pick off weak minions with your Q and use spirit flare against large bunches to jack up your CS

At the beginning of the game your passive helps you stay alive in fights.

PROS
-Nasus has high durability in fights due to his ult and passive
-Nasus is good at escaping ganks and saving peoples lives by baiting the other team away
-Nasus has high sustain
CONS
-Nasus is a late game champion and can struggle early game
-if you don't farm correctly you can struggle in fights
-Nasus doesn't have high burst
-Nasus can use large amounts of mana

Nasus is your late game champion that needs CS but when he does owns it up. Nasus is a underestimated champion and likely wont be banned in ranked or tournaments. Also this makes him a more likely candidate to be buffed in the near future.