In this guide I am using these links in general, I will talk about them more in the guide itself but here they are for quick acess

Lets begin with preparing the files, you will need at minimum 3 files in order to upload your modpack
icon.png - your icon that will be on the mod itself
README.md - a readme (can be empty)
manifest.json - a json file that sorts all of your mods content into one

Your icon.png MUST be 256x256 in order for it to be uploaded.
README.md as written above can be empty but its for instructions or extra details you wanna write down

Manifest.json is the main part of the mod, heres a template of it and we will explain what everything means

• Name: "Name of your modpack"
  
• version_number: MUST BE ABOVE THE VERSION YOU HAVE NOW IF YOUVE UPDATED IT
  
• website_url: can be any URL
  
• description: a description to say what your mods about
  
• dependencies: a list of mod names that exist, in this example you can see "BepInEx-BepInExPack-5.4.2100"

This will be your list of mods, you might be asking how you can get them? its really simple

you will need to take this string and add " between them
DONT FORGET EVERY LINE YOU GOT DOWN YOU NEED TO PUT A COMMA
this means if you add this mod your manifest.json needs to look like this now.

You can always use Manifest Validator to make sure your .json file is proper and with no errors[thunderstore.io]

Now for the last part, to upload your mod you will need to go to here[thunderstore.io]
one there you will need to create an account in thunderstore and then a team.
go to this url right here[thunderstore.io]
Click on create a team and choose a name of your liking

Finally we go back to the previous link[thunderstore.io]
and select your team, community should be LETHAL COMPANY and categories are by the mods you choose, I usually pick

• Modpacks
  
• Server-side
  
• Client-side

You can use this image as a reference, finally upload your "modname".zip file and click submit and you're pretty much done!