Welcome to the forums cycob!
I see those kinds of errors in Ubuntu all the time. Usually it is for one of two reasons (but we need more info from you):
1. Using an Ubuntu release that is "end of life" and unsupported. Click here to see whether you are using a supported or unsupported release: https://wiki.ubuntu.com/Releases
2. Adding unsupported third-party "repositories" or software sources that are not compatible with your Ubuntu release.
Here is a Terminal command that will give us useful info about your software sources. If you can copy & paste the output from this command, it will help us help you troubleshoot:
sudo apt-get update
Also, please answer s.verma's questions!