If you installed tomcat successfully, you may have seen tomcat main page from browser http://localhost:8080/ URL. (Otherwise, you need to check tomcat installation first.)
I guess you may have built jar by fallowing above sites that you mentioned. I am wondering whether you applied the jar into your tomcat or not because you mentioned same result from any other projects. You need to apply jar or war into your tomcat in order to apply java program.
Here are links that I wish they might be helpful to you.
Packaging war : How to make war file in EclipseHow to make war file in Eclipse
Tomcat - war file deployment : https://www.youtube.com/watch?v=9X9DA8oVodk