If you only have one series of points (x, y, error) then you can use the default errorbar function, as per the examples on the help page below:
http://www.mathworks.com/help/techdoc/ref/errorbar.html
If you have multiple series to plot, you'll probably have to use the hold function (remember to turn it off if you need to replace the plot):
http://www.mathworks.com/help/techdoc/ref/hold.html
As for your other question about getting started in MATLAB GUI, I replied a while ago to another poster facing a similar predicament in a different thread (and some of the advice there may be helpful for you, as well):
https://www.physicsforums.com/showthread.php?t=492673
Don't let it daunt you, and remember that the Mathworks has incredibly complete documentation and tutorials. When MATLABdude is a MATLABdud (which actually happens quite a bit), there's always the Mathworks documentation site (and other posters who didn't actually sign up with a username containing the name of a copyrighted program that they're not affiliated with).