It would be helpful if you told us the model of your garmin device.
In the general course with BaseCamp running on your PC you would merely connect your GPS using a USB cable, wait for BaseCamp to read and index the maps on your device (may take a long time the first time it is connected), then identify your device in the lefthand pane of BaseCamp and then drag and drop its data into the BaseCamp My Collections folder.
Thanks, it's a Nuvi 1390. so far I have downloaded basecamp, connected the sat nav and transferred/stored my saved waypoints/favorites + accessed Google earth via basecamp so am now able to view them on Google earth which is what I originally wanted to do. Now I want to suss out how to create routes, can I do this on Google earth and put them onto basecamp first then the sat nav?? thanks.
Unfortunately your 1390 is not capable of multi-point routing. So you could create a route in Basecamp and send it to the Nuvi, but it will just be ignored. You need a different model GPS to use route planning. The 1490 supports it, for example.
The best you can do is to create a route on the unit itself with one via point. Do a Where to, select your final destination and then Go. Once the GPS is navigating that route do another Where to, and Go ... you will be asked if you want to set that as a final destination or a via point.