In order to share your work and make the your Unity projects available for others, the best way to do this is by uploading it onto a git repository. For more information, see Git Overview and Unity Overview.
Useful links:
.gitignore file. This is important because many of the files in a Unity project are recreated on startup and therefore should not be included in the Git repository.
Alternatively, you can initialize a new repository from within your Unity project folder, which is probably a bit better practice, but in this case make sure you make a backup first, in case anything goes wrong. For more info, see git quick reference guide. For a guide on how to do this, see here.
manifest.json file. This file lists all the packages that are required for the project. Unity will automatically download these packages (if free) when their files are missing when the project is opened. Otherwise, you will receive a prompt.
Some tips if your project seems to be messed up:
# This .gitignore file should be placed at the root of your Unity project directory
#
# Get latest from https://github.com/github/gitignore/blob/main/Unity.gitignore
#
/[Ll]ibrary/
/[Tt]emp/
/[Oo]bj/
/[Bb]uild/
/[Bb]uilds/
/[Ll]ogs/
/[Uu]ser[Ss]ettings/
# MemoryCaptures can get excessive in size.
# They also could contain extremely sensitive data
/[Mm]emoryCaptures/
# Recordings can get excessive in size
/[Rr]ecordings/
# Uncomment this line if you wish to ignore the asset store tools plugin
# /[Aa]ssets/AssetStoreTools*
# Autogenerated Jetbrains Rider plugin
/[Aa]ssets/Plugins/Editor/JetBrains*
# Visual Studio cache directory
.vs/
# Gradle cache directory
.gradle/
# Autogenerated VS/MD/Consulo solution and project files
ExportedObj/
.consulo/
*.csproj
*.unityproj
*.sln
*.suo
*.tmp
*.user
*.userprefs
*.pidb
*.booproj
*.svd
*.pdb
*.mdb
*.opendb
*.VC.db
# Unity3D generated meta files
*.pidb.meta
*.pdb.meta
*.mdb.meta
# Unity3D generated file on crash reports
sysinfo.txt
# Builds
*.apk
*.aab
*.unitypackage
*.app
# Crashlytics generated file
crashlytics-build.properties
# Packed Addressables
/[Aa]ssets/[Aa]ddressable[Aa]ssets[Dd]ata/*/*.bin*
# Temporary auto-generated Android Assets
/[Aa]ssets/[Ss]treamingAssets/aa.meta
/[Aa]ssets/[Ss]treamingAssets/aa/*
# 3D models
*.3dm filter=lfs diff=lfs merge=lfs -text
*.3ds filter=lfs diff=lfs merge=lfs -text
*.blend filter=lfs diff=lfs merge=lfs -text
*.c4d filter=lfs diff=lfs merge=lfs -text
*.collada filter=lfs diff=lfs merge=lfs -text
*.dae filter=lfs diff=lfs merge=lfs -text
*.dxf filter=lfs diff=lfs merge=lfs -text
*.fbx filter=lfs diff=lfs merge=lfs -text
*.jas filter=lfs diff=lfs merge=lfs -text
*.lws filter=lfs diff=lfs merge=lfs -text
*.lxo filter=lfs diff=lfs merge=lfs -text
*.ma filter=lfs diff=lfs merge=lfs -text
*.max filter=lfs diff=lfs merge=lfs -text
*.mb filter=lfs diff=lfs merge=lfs -text
*.obj filter=lfs diff=lfs merge=lfs -text
*.ply filter=lfs diff=lfs merge=lfs -text
*.skp filter=lfs diff=lfs merge=lfs -text
*.stl filter=lfs diff=lfs merge=lfs -text
*.ztl filter=lfs diff=lfs merge=lfs -text
# Audio
*.aif filter=lfs diff=lfs merge=lfs -text
*.aiff filter=lfs diff=lfs merge=lfs -text
*.it filter=lfs diff=lfs merge=lfs -text
*.mod filter=lfs diff=lfs merge=lfs -text
*.mp3 filter=lfs diff=lfs merge=lfs -text
*.ogg filter=lfs diff=lfs merge=lfs -text
*.s3m filter=lfs diff=lfs merge=lfs -text
*.wav filter=lfs diff=lfs merge=lfs -text
*.xm filter=lfs diff=lfs merge=lfs -text
# Fonts
*.otf filter=lfs diff=lfs merge=lfs -text
*.ttf filter=lfs diff=lfs merge=lfs -text
# Images
*.bmp filter=lfs diff=lfs merge=lfs -text
*.exr filter=lfs diff=lfs merge=lfs -text
*.gif filter=lfs diff=lfs merge=lfs -text
*.hdr filter=lfs diff=lfs merge=lfs -text
*.iff filter=lfs diff=lfs merge=lfs -text
*.jpeg filter=lfs diff=lfs merge=lfs -text
*.jpg filter=lfs diff=lfs merge=lfs -text
*.pict filter=lfs diff=lfs merge=lfs -text
*.png filter=lfs diff=lfs merge=lfs -text
*.psd filter=lfs diff=lfs merge=lfs -text
*.tga filter=lfs diff=lfs merge=lfs -text
*.tif filter=lfs diff=lfs merge=lfs -text
*.tiff filter=lfs diff=lfs merge=lfs -text
# Collapse Unity-generated files on GitHub
*.asset linguist-generated
*.mat linguist-generated
*.meta linguist-generated
*.prefab linguist-generated
*.unity linguist-generated
*.aar filter=lfs diff=lfs merge=lfs -text