Search wikipedia to get a first impression on what is source control. Please also check application lifecycle management (ALM).
Once you understand what source control is, I suggest to get started with Requirements gathering.
Please drill down on the different topics, or select the tag/category on source-control to have an overview on articles.
Once you get a basic feeling, read some comparisons to select the source control you want.
From the menu, one can also access the remaining pages on different tools and tool selection process.