error: Error establishing a database connection

i need help from everyone. my english is not good , but i hope everyone understand my problem. i am a new user on wordpress and download the ne software from wordpress. i give the name, passworth etc. in the field i must for registered. now i open the site and have this error:Error establishing a database connection. i don`t know what i must doing. can everyone, at the best much visitors help me.
thanks for a feedback