Q: can you help me how to install applications on my ipod ma623c

You have the origina, 1G iPod. those can m;y go as high as iOS 3.1.3

Connect the iPod to your computer and update via iTunes as far as your iPod model allows

iOS: How to update your iPhone, iPad, or iPod touch

A 1G iPod can go to iOS 2.2 via iTunes and iOS 3.1.3 via

Purchasing iOS 3.1 Software Update for iPod touch (1st generation)       

  https://buy.itunes.apple.com/WebObjects/MZFinance.woa/wa/touchLegacyLandingPage

However, there are not that many apps compatible with 3.1.3. To find those more easily:

iOSSearch - search the iTunes store for compatible apps.

Vintapps 3.1.3 - paid app.

Apple Club - filter apps by iOS version.