There are certain things about the bible I have a tough time with, take for example the following verses. Moses speaks to his troops after a battle in which they won , " Now kill all the boys. And kill every woman who has slept with a
man, but save for yourselves every girl who has never
slept with a man." Numbers 31:17-18 .
I'm very troubled by this verse..

Please someone should help me understand it

Why not try understanding hundreds of other verses that will help you? Are you a sinner? Do you know Jesus? Those should be more important to you sir.

This site offers an explanation, but it is a bit lengthy:
http://christianthinktank.com/midian.html

Do you own a church? List your church on Nigerian church directory https://www.naijachurches.com.ng/

nairalandankrah:
There are certain things about the bible I have a tough time with, take for example the following verses. Moses speaks to his troops after a battle in which they won , " Now kill all the boys. And kill every woman who has slept with a
man, but save for yourselves every girl who has never
slept with a man." Numbers 31:17-18 .
I'm very troubled by this verse..

Please someone should help me understand it

Nothing to understand there or try to make sense of, except that it went down that way or manner, back in the days, because of divine judgement or retribution, if you like

Now like Image123 has advised in his comment, there are more important scripture to try get understanding of

nairalandankrah:
There are certain things about the bible I have a tough time with, take for example the following verses. Moses speaks to his troops after a battle in which they won , " Now kill all the boys. And kill every woman who has slept with a
man, but save for yourselves every girl who has never
slept with a man." Numbers 31:17-18 .
I'm very troubled by this verse..

Please someone should help me understand it

jihadists style, kill the boys and keep the girls as sex slaves.