you could have been trying to put the plug in upside down, they are normally a simple push in, have a close look at the socket the top should have a slim plastic lug and a very narrow space, below the lug should be a space about a millimeter wide.
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The reverse is in the plug you should see a plastic lug which should be fitted under the Socket lug.
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Please be aware that there is another type of socket called "Firewire" which in simple terms is flat at one end and pointed or apex at the other "DO NOT" try to fit USB connections in them.
the howstuffworks.com web site can give you a few helpfull guides