Percona has a lot of great guides for getting started with the basics of Xtrabackup:
I would start by taking a look at those guides, and then see what specific questions you have.
As far as performance goes, generally speaking, the larger the dataset, the quicker Xtrabackup would be when compared to mysqldump (simply based on the way they work; not that one tool is “better” than the other). That aside, these tools have different uses/benefits in general, so I would not necessarily pick one over the other just based on performance.
Below is a section from the official MySQL docs that talks about the various general backup types. When reading it, just know that when they talk about “MySQL Enterprise Backup”, you can substitute that with Xtrabackup, as Xtrabackup basically works the same. This will help you decide what type(s) of backups you really need (i.e. mysqldump=logical backup, Xtrabackup=physical backup).
Additional mysqldump info: