You can simply call a script by its filename. So if we have this single lines of code in a script named sqrA:
B = A .^ 2;
we can call it from another script simply by calling its filename:
A = 1:4;
sqrA
disp(B)
which displays this in the command window:
1 4 9 16
Although this is obviously a pretty silly example, and calling such simple scripts like these ones is not recommended. Instead you should learn about functions, which are much more versatile, and allow control over the input and output arguments. You can also put multiple functions in one file, whereas you can only have one script per file.
If you are not sure what a function is, then read about the differences between scripts and functions.
You should probably work through these tutrials, which cover most of these basic concepts in MATLAB:
