A full CAN message consists of a FRAME ID and a MESSAGE. You're probably going to have to Reverse Engineer the CAN messages to find out which message you want to put on the bus. The answer there also deals with how to read messages as well.
As far as specifically addressing the ECU, not sure how you would do that without having the official documentation, or reverse engineering and finding a message that is truly addressed to the ECU. CAN messages do very specific things, so I would be careful what you send if you don't know what you are doing, as you could seriously damage the vehicle. That being said, the ECU has a CAN ID just like every other device on the network, so it will read in whatever is addressed to it.
Just an FYI, a CAN BUS is similar to a mesh network, or an ethernet subnet, every device will see all the traffic, but will only act on traffic that is specifically addressed to it.