error bars

Can any one please walk me through how to make error bars? I seem to get it wrong every time I do it and my TA never showed us how to do error bars! Is it just the literal value I get for my error in cm for both x and y or so I have to measure it in some way compared to my axis and then plot them?
Any help is appreciated.
thank you.

The errors for the X-values should be shown around the point. Same goes for Y-values. Let's see if I can show it here and have it make sense.

The error for X is 1, the error for Y is 2

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The vertical dashes should be above and below the X
Where "X" is your point. Refer back to the Error and Uncertainty manual to see a better example of it towards the end of that manual.