It's really very simple, Samuel. Judgment is a fact of life. It's not a question of whether you'll judge people on matters that need to be evaluated and dealt with, but how and why you will do it. The Lord was clear on this:
“Judge not according to the appearance, but judge righteous judgment” (John 7:24 KJV).
Otherwise, how can you tell true brothers from false? If you're His, does the Lord want you to congregate with workers of darkness, Satan's emissaries who deceitfully transform themselves into His servants (2 Corinthians 11:13)?
When the Lord speaks of not judging others, He's addressing judging with a carnal heart and selfish motive - a beam in the eye that always boomerangs on the one who judges thusly:
“Judge not, and you shall not be judged. Condemn not, and you shall not be condemned. Forgive, and you shall be forgiven” (Luke 6:37 MKJV).
“And why do you look at the splinter that is in your brother's eye, but do not see the beam that is in your own eye? Or how can you say to your brother, Brother, let me pull out the splinter in your eye, when you yourself do not see the beam that is in your own eye? Hypocrite! First cast out the beam out of your own eye, and then you shall see clearly to pull out the splinter that is in your brother's eye
” (Luke 6:41-42 MKJV).
Our whole site is full of instruction on righteous judgment, but perhaps these writings in particular will help you get started on the matter:Judge Righteous JudgmentDisdaining None, Judging All, for Good