Help with humminbird helix 5 g2

I guess i am not tech smart enough to set up this unit. I bought a lakemaster sd card. and my computer has no way to receive the sd card, so i call the support people at humminbird and they say that I have to set default on the basemap first ????? then download the sd card. ??? I am realy confused at this point HELP
please. 419 688-7698 thanks john

page 20, 21, 117 & 127 of your operations manual will tell you how to insert sd card & set up chart. Go to Humminbird.com & Select proper manual for your unit.