Here are simple instructions that will do what you need nearly every time. In some cases you might need to get more involved with adjusting the secondary but try to avoid that if possible. Most of the time you will just need to tweak the primary mirror a little and you will be good to go.
Many well-meaning instructors will have you adjust the secondary as the first step in collimating your telescope. Most of the time that step is not necessary and it just adds complexity for a beginner. My approach is designed to get you up and running quickly without bogging down in needless steps. The techniques I teach you here will work for you 95 percent of the time. You can pick up the additional techniques later if you need them by watching my second video on the subject.
I am a retired Astronomy Professor. I do not make any money or benefit in any way from my recommendations. Unlike many Youtube reviewers, I am not an Amazon affiliate. I make nothing when you make a purchase.
Links to more detailed instructions:
My second collimation video on adjusting the secondary mirror (if necessary):
https://youtu.be/Mk0S5OMn8aA
Gary Seronik (BEST): https://garyseronik.com/a-beginners-guide-to-collimation/
Sky and Telescope (SUPERB):
https://skyandtelescope.org/astronomy-resources/how-to-align-your-newtonian-reflector-telescope/
Highpoint Scientific: https://youtu.be/ILJ_0FkFAwU
Small Optics: https://youtu.be/KADpZ_XZkS8
Using a collimation cap: https://www.youtube.com/watch?v=kwzqizxAXdY
Here is the best collimation device for the beginner (Cheshire Eyepiece):
https://www.amazon.com/gp/product/B00OXKI3N4/
Best Beginner Telescopes: https://youtu.be/BlzKZ28P7sY
How to Select a Beginner Telescope: https://youtu.be/0SIjhcePcNM