First, be careful when playing with Simply Accounting data. Make sure you understand the database before adding or updating anything in it.
To connect to the MySQL server, you first need it to be running. This is the case only if Simply Accounting is running or another third party is running and connected to the database. The Simply Accounting Connection Manager service start the MySQL when it is needed and stops it when all connections are released.
Then, the port number to access the database is not the usual MySQL port number. By default, the first database open will be assigned 13540. Subsequent database will follow (13541, 13542, ...). The database name is 'simply' and you must use a user with third party access right to open it (see Set up user in Simply).
That pretty much covers it.