General Apps Query

[Bear in NM]

Folks,

I hope this is the correct forum. I am wondering if someone could give me some basic help on Apps. I am new to the droid concept, and have downloaded a few free apps, and saved links to my new Google account. Got that down.

My questions are about backing up actual app source data, perhaps on my SD card. Is on-line with my phone the only way to install an app? With paid apps, I am assuming that I have to use a credit card. Will I then be able to have the app sent to me and saved either on my SD card or computer. Is there some other method involved with paid apps?

My concern is based on either having to exchange my phone, or perform some type of reset. Trying to understand the basic concepts before I get too far gone on the wallet.

Thank you,

Craig