I have a yellow and here is what I do.
I hold the enter button (lower left hand side) in and this "marks" a waypoint. Hold it in long enough for the page to change to the waypoint page.
Then use the up/down keys (upper left hand side) to move to cursor to the coordinates and press the enter button again.
You then have to go through the slow rendition of inputing letters and numbers by scrolling with the up/down keys. Press the enter button after each correct letter or number. The unit automatically indexes to the next space. Press the enter button again to activate, etc, etc, etc. It can take a while.
Once you have the coordinates in, you can move to the name of the waypoint and change that in a similar manner.
You can also change the symbol for the waypoint too.
Hope this helps. I have not invested in a cable or software though I did download cachemate for my Palm.