Medved Trader can connect to various market data sources, both brokerage-based and independent, and the list keeps growing as we're adding more to the program. Each source can provide different type of data - Level I, Level II, Backfill (both intraday and historical), and Option Chain data.
In order to connect to these sources, you have to specify connection parameters (for most data sources that would be a login name and password) in Medved Trader. You do that in Settings - Data Sources - Configure Accounts. The parameters vary depending on the data source. For some, MT will redirect you to the source's web site to log in.
NOTE: the login information you enter is used by MT to communicate to the data source directly. None of this communication goes through our (Medved Trader's) servers. It is exactly the same as your web browser communicating to your broker's web site.
Once the site and its login parameters are set up, MT will remember them and will not ask for them again unless the Remember Password is unchecked. In that case, it will ask you for the password every session.