How to load and process EEG txt/mat/edf/dat file ?

Hello, I need some tips, direction on how to load files that contain EEG data. I tried with loading .txt or .mat format load('eeg.txt/mat'); x=data(;,) but whatever I do I get the error "invalid first data argument" or "invalid function ar data"; I also tried function plotATM, to load edf file type, from here but I don't know what do to with it after the plot is displayed. .dat file is a little bit to complicated for my understanding ... I need help big time. I read some of the questions and answers from here but still need more information.

Thanks in advance!