Which organelle carries substances to other parts of the cell?

The answer will be Endoplasmic Reticulum (ER).

It is a kind of channel that carries substances, such as proteins, oil droplets, water, to other parts of the cell.

Well, to make it easier, endoplasmic reticulum is actually a fancy way of saying "cellular highway". I will explain to you why. I always like to study BIOLOGY relating our activities and our stuff. 

Okay, let's push aside cells. Let's think of us, humans. We can't stay in one place, we gotta moving all around the city. What do we use for moving around the city: either roads or sidewalks or footpaths.

Just like that, a cell also has a medium or road or a channel where all the substances can move around the cell. Well, its ER! So, from now on, everytime you are struggling with this difficult, L O N G word, just replace it with "cellular highway". The ER is like a water pipe, too. Water flows through it. Here, cellur substances flow through it. The ER is connected to the nucleus.

SUMMARY:

1# ER aka Endoplasmic Reticulum is a kind of channel that carries substances, such as proteins, oil droplets, water, to other parts of the cell.

2# Try thinking it easy: replace it with "cellular highway".

3# It is much like the roads or sidewalks, we walk on.

Both prokaryotic and eukaryotic cells have ribosomes and cell membranes