Answered How to load data from and .txt file?
To read a tab delimited ascii file while skipping the first row, try:
data = dlmread('Spill.txt','\t',1,0);
Answered How to set period (t=0 becomes t=-4)
might depend on what and how you're plotting. For the simplest case you can just do this...
t = 0:100;
data = somefu...