interaction with signals

i want to experience(see) how the two signals are added or multiplies or scaled will be.i cannot install matlab to view that since my comp is not that much capable of .so please say me any site for that or any small software to see those operation visually .Thank you

Here is a visual simulation of adding multiple f and select amplitude and phase of each and see result.

https://www.falstad.com/fourier/e-beats.html

Also harmonic content of triangle or any shape signal
https://www.falstad.com/fourier/e-triangle.html
https://www.falstad.com/fourier/e-index.html

Multiply not shown.
But more https://www.falstad.com/mathphysics.html