'Cognition' is a word used to denote a thought or belief, and 'restructuring' involves challenging a cognition by looking at the evidence for or against it.
The basic idea behind cognitive restructuring is that thoughts are not facts.
You need to consider whether the thoughts you are having are true and to consider whether there are any other ways of thinking about a particular situation.
At first this can be a real challenge: we often believe what we think and don't question our own thoughts. However, often our thinking is biased and with perfectionism it can be biased towards thinking negatively or harshly about yourself.
Thoughts vs Feelings
To become aware of your thoughts, it is useful to ask yourself
"What is going through my mind?"
Sometimes thoughts can be statements, such as "I'm a failure", but sometimes you might also have images or someone else's voice.
For example, you are thinking about going on a first date. The thoughts you are having are mental pictures of yourself shaking with anxiety, spilling a drink on yourself, or not knowing what to say.
It is useful to write down the thoughts and images that come into your mind so you can gain more insight into:
Which thoughts occur most frequently
What triggers you (occurs right before an event) to think certain thoughts
How positive or negative those thoughts are
Feelings, on the other hand, are your emotional reactions or the emotional states we all experience. Some common emotions include:
Plutchik's Wheel of Emotions
Typically feelings can be captured by one word whereas thoughts are longer statements.
For example, you might say something like "I feel my partner was rude to me and it was unnecessary for them to upset me." The feeling you experience is sadness, but this type of statement is actually expressing a thought.