I am confused on what the difference is between webscalesql and mysql. From my understanding webscalesql is a branch of mysql. Does this mean that webscalesql is a subset of mysql, so it is better to download MySQL rather than webscalesql as the changes made in webscalesql will be merged? If so, why would anyone download webscalesql?
Webscalesql is a project born in order for those organizations that maintain their own MySQL patches to use, and review each other's code. So engineers from facebook can improve twitter patches can improve Google patches and so on. It is necessary for now at least, because its seemingly difficult for Oracle to accept, QA, test and ship external code. Note the use of "seemingly". Some would argue it is not. Webscalesql is not supported by anyone so I would advise against running it in production environments without your own MySQL engineering team. Oracle, Percona and MariaDB should be the direction to look to for an implementation.
webscale (https://github.com/webscalesql/webscalesql-5.6) is a fork of mysql implementing, apparently, facebook's mysql patches. These same patches are slowly making into many of the mysql forks out there.
If you are a beginner, simply use MySQL. Once you have a better feel for the product, and (perhaps) your dataset grows to Facebook-size, then consider the various other products that help with serious scaling.
99% of users never need to go beyond the basic MySQL (Community MySQL, MariaDB, Percona's MySQL).