If you haven't done it already, please set up your account for Git/Gerrit and other tools. You can find help at Getting Started steps.
Next, you will need some packages: git and git-review
Then git clone the project (with your ssh key). For example, to propose a patch to BGS (git repo name genesis):
git clone ssh://<yourname>@gerrit.opnfv.org:29418/genesis
Prepare for git review
git review -s
If you run into troubles, like "We don't know where your gerrit is. Please manually create a remote named "gerrit" and try again." you may need to manually add a remote
git remote add gerrit ssh://<yourname>@gerrit.opnfv.org:29418/<RELEVANT_REPO>.git
…do the work on files…
git add . git commit --signoff --all
Add a description to your commit based on below etiquette.
Send your commit for review.
If you need to update a previous commit, you can use:
git commit --amend