"Someone who has never seen a computer understands this"
Am also like Mr. V ... don't understand what you are trying to do.
"... do not want one person login from one computer at the same time with multi account"
So one person has two accounts in your Moodle? OR you think two persons are using the same computer to login to your moodle with different credentials?
If the latter ... the only way have seen that to be possible is when the computer being used by 2 persons had a 'buddy card' (Windows only) ... 1 computer, but 2 monitors, 2 keyboards, 2 mice (per person). But, the IP address acquired by the computer is the same.
Maybe someone else can explain better than I?
Best of luck!