To create and manage MySQL databases only over the command line can be quite challenging. You may know to the browser-based tool “phpMyAdmin”, but this tool has some limitations (e.g. no visual data base design)
To overcome this problem, you can download the MySQL Workbench from https://www.mysql.com/de/products/workbench
Install the program, start it and add your database credentials using the plus right to “MySQL Connections”. Caution, maybe not every database can be accessed directly throw the internet, many databases listen only to localhost for security reasons. If this is the case, use Standard TCP/IP over SSH to let MySQL Workbench to create an SSH tunnel for you.
Now you can use the MySQL Workbench to create and manage your databases.
The answer is: it depends.
It depends on the programming language you are using and partially on the database you are using.
Most of the databases are services running on a web service. We can communicate with them using a special protocol, while we know the address and the port of the server where it runs. There are also databases stored in files, where we specify the target file.
Most of the programming lanugages and frameworks provide a "Connector" for databases, which allows us to communicate with the database. Of course you need to check if your programming language has a driver for the database type you want to connect to. Some frameworks or programming languaes also offer a higher level control structures called object-relational mapping, where the user can easily read or write some objects defined in the project.