The book I used to initially learn Esperanto translated "jen" as "behold".
So "behold my book!".
Why is it ok to take out estas?
The word "jen" is usually used without a verb. It's used to present things; it doesn't literally mean "here is" (that would be "ĉi tie estas"), it's just a word without any real translation in English.
Behold, it's Jen!
What is the difference between tien and jen?
Jen is an interjection used for emphasis