This can be a difficult topic to get our heads around so try this link to go over it again.
There is a video and 3 activities to go through.
Here are some other examples to help this stick in your mind.
Active: Simon carried out the action - he comes first in the sentence. This is the 'snitchy' voice - "HE DID IT!"
Simon broke the iPad.
Passive: Action first and I may or may not say WHO did the action. Newspapers use this technique a lot.
The iPad was broken.
The iPad was broken by Simon.
Here is another explanation...
Also, if you haven't seen the KS2 music assembly yet, check here. I KNOW you will love the songs this week. Take a listen.