To uninstall applications : Go to Options > Advanced Options > Applications, scroll to the application you wish to delete, press the menu key and select delete.
As for adding applications. There are a few ways, if it is a .jad file, browse to that URL from your BlackBerry browser and it will prompt for you to download. Otherwise it will be a .cod and .alx file and you will need to install those through Desktop Manager.
And welcome to the forums.