for loop and array

How can I run a for loop to read 3 different files loaded already on my workspace. Add the values on file 1 to file 2. Extract from another file the data and add +600, add that new data to an array and plot it. Any help with the code for this is really appreciated!

for j=1numTrials
    trials=sprintf('trial_%i',j);
    trialNum = num2str(j);
    StartWalkFrame(j,:) = [str2double(trialNum)] %read start frame
    EndWalkFrame(j,:) = [str2double(trialNum)]  %read end frame
    StartAndEnd = sum(endframe) to startwalk  %add endframe to startwalk
    GSRData600 = extract  %extract GSR data and add 600 frames
    %add data to an array
end

[Stephen23]

Duplicate: https://www.mathworks.com/matlabcentral/answers/1897970-for-loop-to-read-different-files