database config

hi guys

i just created another database using db config assistant
the creation is succesful ...after the creation messages pops up to check the create.log...im not familiar on whats in the log
anyway when i start my oracle im expecting to connect with the oracle database but i'm not instead i'm connected to the 1 that i create.....how can i connect to oracle DB and swicth to another ..i didn't do anything about the .log (do i have to do anything about the log file???)..

thank you
pls.help