Allowing the emotion

I don’t understand the process of allowing an emotion/feeling. What does that entail? Like for example shame is uncomfortable – do I just sit and experience what it causes in my body. How long should I do that? For example after an incident or circumstance —-> you have a thought—-> that causes the feeling of shame. Then I forget about it. Every time I have the think of the incident—> it induces a feeling of shame. Do I then again experience it?

I would like some guidance on this process of going through the feeling/emotion.