How to check mssql version installed + install option

Open a cmd and type :

sqlcmd
select @@version
go
exit

Default instance is that you connect just by specifying the server name (eg, MYSERVER), whereas a named instance will require an instance name as well (eg, MYSERVER\SQL2005).

Clients can connect to the default instance using only the host name over the well-known 1433 port.
To connect to a named instance, clients specify the host and instance name (e.g. "MyHost\My_Instance") and the SQL Server Browser service returns the port the named instance is listening on.