You should familiarize yourself with a Version Control System. Most people are using Git these days, however, there are other systems such as
- Subversion
- CVS
- Mercurial
And plenty of others.
The way I typically see WordPress projects in Version Control is the following:
- Everything in your /wp-content/ should be in your repository
- Things like wp-config.php and /wp-admin/, etc, should generally not be in your version system for a few reasons:
- Putting your wp-config.php in version control means you are storing things like
DB_PASSor your salts in a repo, which can be bad if you don’t want other collaborators or possibly the public seeing that information (depending on where you host your code) - You generally don’t need or want to control core WordPress files as you will probably be replacing them when new versions are released, and otherwise you shouldn’t be modifying these files, hence no need for VCS.
Next, you need a way to hook your versioning system up to your server. This will depend on what you use for VCS and where your site is hosted, etc. Generally, you’ll want some kind of task that can “listen” for changes in your repository and automatically pull the latest changes, prepare your files, and push them up to your live server.
Your question is really too broad to give you anything concrete to go on, I would just learn something like Git and familiarize yourself with good workflow practices (how to branch and merge, how to avoid and handle merge conflicts, etc).