how to connect speaker to the computer?

Answer 1

Assuming you mean proper PC / walkman type speakers . . .
plug the small 3.5mm stereo plug on the end (usually coloured green these days) into the matching socket on back of PC, also usually green now.

Enjoy the music.

IF you mean proper "BIG SPEAKERS" from a normal stereo, you can't, you'd need to take the output from PC to an amplifier first, then to the speakers.