How to link slide to a graph

I'm actually very new to Matlab but I'm doing a school project and i need the make the slider work inorder to complete my project ASAP. The problem now is that i not very sure of the code used for the slider and i don't really understand the code i found online. I will have to plot the graph by the value from the file the user select to display some EEG signal. Since it's ever changing value. So i'm not very sure how to do it.