Show us what you've tried...this is trivial from the links I've shown you before.
The only issue is you will have to convert the text fields to numeric arrays, but this is also pretty-much dead-ahead string interpretation...the hardest part will be ensuring the user enters valid text and there are same length vectors, etc., etc., etc, ... You might want to reconsider how the user is to specify the number and values of the points to make certain the input returned is valid instead of trying to parse what could be free form input...
But, given your example...
load=str2num(app.yText.Value);
t=str2num(app.xText.Value);
plot(t,load)
is the bare bones of it -- of course, as noted, the above will need to be in a |try...catch..end] block with a lot of error checking to be able to be sure you have actual data; the free form user input is going to be a lot of trouble.
You would do the user a big favor in providing more context -- just an "X" and a "Y" is pretty hard to tell about although maybe there is sufficient surrounding other information it makes more sense than just standing alone. But, I would suggest using meaningful labels including telling the user what units of time and load are expected -- unless those are being set somewhere else, too, of course.
