Q:

How to know where my MySQL database is being hosted and how can I access it? 

I have the following information to a SQL database

Server : MyUserName.mysql.db
User : MyUserName
Password : MyPassWord

I am a little noob in this context, so I have some questions:

How to know where is hosted my database?  Is it in mysql domain? ( Isn't that the type of database?) 
How can I access it and visualize it? 

A:

To begin with, you need a CLIENT to be able to access your database.  For MySQL, you can use either Workbench or MySQL CLIENT (the last giving you command-line level access). 
Second, and according to your information, the server is MyUserName.mysql.db so if you try to PING that server you should get some response. 
Third, MySQL has a default port number so you need to configure your client to access that server though that port (if I'm not mistaking, 3306). 
You will also need access credentials to your database. 
Your DB administrator should be able to provide all the information you need.