Welcome to Android Central! That's why when you enter your contacts into your phone, you should make sure they're being saved to your Google account, and not the local Phone account. The latter doesn't sync anywhere, while the former immediately get synced to your Google Contacts in the cloud, and are therefore accessible anywhere that you're logged in with your Google account. Phone account contacts have to be exported as a VCF or CSV file if you want to back them up or transfer them to the computer.
For notes, it depends on what note-taking app you're using. Most preinstalled note apps don't sync anywhere, and many don't even give you easy access to your note files to transfer or backup. I always recommend using a cloud-based cross-platform note-taking app, like Google Keep Notes or Evernote.