Self-updating apps aren’t a big thing on Linux, so the Windows way isn’t an option…
The signing key is important for security reasons, so you definitely need to add that. After adding the repo you can just use Synaptic or whatever app store thingy Ubuntu uses.
Most of the time you shouldn’t need to fiddle with the command line and the apps you will need are available through the Software Centre and the entire process will work like on Windows.
For me, Linux was the first operating system I used that had an app store or software centre and I was pretty glad to not need to…