Not found 404

I installed this plugin throu WP plugin manager, and it seems that all is Ok. Every time I try to use this plugin — upload picture, make post call it main, and go to my_site.domain/imagemap_area/main/ I got 404.

What is wrong? What kind of information do I need to provide to help to solve this issue? Or else, please, point me, where am I wrong. Thanks.

https://wordpress.org/plugins/imagemapper/