ECE is all about electronics and how the different electrical components (Microprocessor, RAM etc) communicate with each other. It has more Physics in it. There is a little programming involved but not much whereas CSE deals with telling these components what to do and when to do it; by programming them. It has a lot of logic involved and Maths too.

To know about both the branches, you can go through the below links -

Electronics and Communication Engineering

Computer Science Engineering

Hope this helps!!!