There are possible sources of confusion here, I expect. As SGilbert points out, the connection between the iPod touch and your Mac must be made using the white cable (USB for your Mac at one end, "Dock connector" for the iPod at the other end). If we are talking essentially about using your Mac to install apps on the iPod touch, then WiFi and Bluetooth are irrelevant here.
Firstly, ensure iTunes is running on your Mac. Once you have plugged the cable into your Mac and then the iPod touch, you will see iTunes become aware of the iPod being attached. If you click on the iPod touch icon, under "Devices" on the left hand side, you will see a summary screen for it. Your software version should be 2.x (most likely 2.2). If it is 1.1.4 or earlier, for some reason, then you won't be able to install any apps until you pay for the upgrade through iTunes. If it is showing up as 2.x, it should automatically install the apps.
While the iPod touch is selected, there should be an "Applications" tab, amongst others (e.g. Summary, Music, Movies, etc.), in the main window. Make sure you enable syncing and that you either sync all (iPod touch) applications or that you have selected specific applications to sync.
On a different note (and potentially muddying the waters!), it is possible to more directly connect the iPod touch to the iTunes Store to download apps. This can only occur, however, when the iPod touch's WiFi is switched on
and you have a wireless internet connection available for it to use. Then you can use the blue "App Store" icon on the iPod touch to browse and download apps without going via your Mac.
If you follow the above, with any luck all should be OK! Let us know how you get on.
