Ok kiddo, so let's say you have a bunch of cool toys (emails) in a big toy box (email server) that you like to play with. But sometimes your friend wants to play with some of your toys too! So you give them permission to take some out of the box and play with them for a little bit.
Now with push-imap, instead of waiting for your friend to ask if they can take toys out of the box, you can just automatically give them permission. This means that as soon as you get a new toy (email), it'll be automatically shared with your friend without them having to ask every time.
Basically, push-imap helps share your emails automatically with other people or devices without you having to manually share them every time. Cool, huh?