1) Incorrect password:
"sysdba" is a role in Oracle, not a username.
You should be able to log in with the "system" username, for which you have specified the password during database creation.
Warning: don't create any tables or views using the "system" account. Create your own account and put all your objects there. System is special, if you put your tables there and load a lot of data in them, you might allocate space to the system tablespace, which is difficult to reverse. If you put all your work under your own account, it is then very easy to throw away everything (just by dropping the user) and start again, but it is more work under the system account. And there are security considerations too.
2) Error during installation:
I believe the files listed are just informational messages about them being installed. As far as I know, they don't belong to the Net Configuration Assistant specifically. If you put these directories in your PATH variable manually, I'd suggest to remove them. It shouldn't hurt, but one never knows.
The Net Configuration Assistant helps you set up listeners and TNSNames; a default listener should be created automatically with your database and you shouldn't need to worry about it now, and the TNSNames are not needed if you connect
locally using SQLPlus and other Oracle tools. In any case, you should be able to run the Net Configuration Assistant from your start menu manually, perhaps it will say some more specific error message.
Do you have some tutorial or textbook to follow? Oracle isn't exactly easy to start with.