I've want to learn GDS systems: Travelport (Galileo, Apollo, Worldspan), Amadeus and SABRE. How can I do that?

Hi,
Apologies for the delay in responding.
The best way to learn is to visit their websites and access learning content.

I am including some links below as an example (some of these may require signing up):
https://amadeus.com/en/training
https://www.travelport.com/products/mytravelport
https://your.sabre.com/sabretraining
https://eportal.travelport.com/sites/GSWS/SiteCollectionDocuments/SGC/Portal/Documents/QRef/Welcome%20to%20Apollo_QR_EN_0407.pdf

You may also benefit from newer direct connections such as IATA NDC, the details for which is on the IATA website.

Some third-party training providers also offer such training, such as OTT, Udemy, etc.

All the best in your learning.
Ananth

Thank you for everything! I will apply all the advice that you have given me.