Go into Mobile networks settings on your phone and make sure Data is off.
As for apps. There are tons and tons of apps, many free you can use.
The simplest way to get them to your phone would be through gmail. Naturally you will need to use your wifi.
Set up a gmail account on your phone, and any apps you send to your gmail account you can install with one click on your phone, directly through gmail.
Apps are usually in .apk format or .zip Most times you can rename any .zip to .apk and They will install fine.
Another way to do this is, to root your phone and have root directy access. They you can use any file explorer (some free ones in the market) and transfter any apk to your phone and navigate to it, and simply install it.