This is the 2768th most frequent Spanish word.
matar
"To kill."
In this sentence, 'matar' is used in its literal sense to refer to ending the life of another living thing, specifically insects.
Ella va a matar a las moscas con un periódico.
She is going to kill the flies with a newspaper.
Here, 'matar' is used metaphorically, meaning 'causing extreme discomfort or annoyance', not literal killing.
Esto me está matando de aburrimiento.
This is killing me from boredom.
'Matar' in this context is idiomatic, signifying to use time in a leisurely manner.