Newbie. How to use JCV file ?

This is for your 1450, right?

The file is too big to fit in the nuvi 1450, so it will need to go on a SD card. (In fact, by choosing to install map updates to a SD card will give you all of North America while installing to the nuvi will give you a smaller map.)

The SD card needs two folders to be manually created: create a garmin folder on the SD card, then in the garmin folder, create a JCV folder.

Now when the nuvi/SD are connected to your computer, copy the large jcv file to the \garmin\JCV folder in the SD card.

Finally, look in your nuvi storage (or if the map is on a SD card, look to the SD card) for a file with a JCV extension. It'll be something like D******A.JCV. This is the small default Junction View file that came with the map update. This needs to be disabled, The safest way to do this is to rename it .disabled; i.e., D******A.JCV.disabled.

Once done, you will always want the large JCV file. The large JCV changes with each map update and the JCV file must be the one that was made for the map version you have. For the 2014.40 map update, the corresponding large JCV file is D3060130A.JCV:

http://www.poi-factory.com/node/42030

The .disabled files will remain and are not removed when you do a map update, so every now and then you will need to go to the nuvi and delete the disabled file.

Before doing any of this, it's very strongly recommended that you have a full backup of all files on your nuvi (or nuvi/SD) to be able to recover a file accidentally deleted.

Shout if you need more help.

Excellent advice you've received so far but please understand that you would never use POI Loader to load a JCV file. POILoader is used only to load .csv and .gpx POI files (Points of Interest files) that can be downloaded from this, and other sites, to your Nuvi. On the Nuvi they become Custom POIs.