Sometimes you see a video on Instagram that you would like to watch several other times later or get a particular info that you would need later, but Instagram only allows you to view them temporarily. Here is how to get them with ES file explorer.

After watching the video on Instagram, minimise Instagram and go to ES file explorer and do the following :-
For elite
users, open /Android/data/com.instagram.android/cache/video
For new/regular users,
(1) Open the folder named 'Android' on your primary memory storage. (It could be on your phone memory or your memory card)
(2) Open 'data'
(3) Open 'com.instagram.android'
(4) Open 'cache'. Open 'video'
(5) You'll see files like 'ab75388y.0', don't be scared (just kidding o). For heavy Instagram users, you'll see a lot of them. Highlight one of them by holding down until there's a blue tick on the right. Then highlight all of them by touching the dash-lined square in the top right and copy them.
(6) You'll need a new folder to paste them in, so go back to the home folder (where 'Android' and all other folders are) and create a new folder by selecting 'New','folder'. Name it 'Videos(instagram)' or something you will remember. Open the new folder and paste them there.
(7) Highlight everything you copied again and select 'Rename'. On the rename dialog, select the last entry box and type 'mp4'.
( Voila! They all become videos.
That's how to do it. If you have questions, feel free to ask.