Contents:
Official git documentation
Atlassian git tutorials
Git - submodule docs
Git - working with remotes
Atlassian - git merge conflicts
Github - resolving merge conflicts from the command line
Official git submodule documentation
Atlassian git submodule documentation
Using submodules in git - tutorial
Working with submodules - blog
CCCma generic submodule overview
Atlassian - Forking Workflows
Medium - Git Forking Workflow
CCCma generic forking overview