Feelings

Great question!
A feeling or emotion start in your brain (from a thought) and are a vibration in your body.  This is different from a sensation, like tired, hunger, or pain, which are involuntary and start in the body.

There are hundreds of feelings, and if you'd like a list, google feelings for examples.  Some of the basic ones are happy, sad, angry, frustrated, disappointed, excited, fear, love, etc.  We feel our emotions differently, and there is no right or wrong way to do this.
Some people are really good at feelings and others are really good at thoughts.  If you're struggling with feeling any emotion, try this:
Be still and notice what you're feeling in your body.
See if you can name the feeling (any 1 word emotion).
Find where it is in your body and describe it in detail (for example, I feel frustration in my throat - it's tight, hot, dark).
Really think about what it feels like and relax into it.
Remember that this feeling is simply coming from a sentence in your brain (a thought).
Allow the feeling to be there until it subsides.
Sometimes we try to resist emotions by buffering with food, social media, shopping, or something else that is creating a net negative in our lives and keeping us from processing the emotion.

The worst thing that can happen to us is a negative emotion.  When we know we can handle any emotion, and that we're here to experience all of them, we're truly living our best life.