Well @Marisa_Smith has a great short video on this 
Streamlit Shorts: How to make a button - YouTube
In short:
t = st.text_area("Write smthg")
if st.button("Summarize"):
# here apply your summary functions to the text input
summary = t.lower()
st.write(summary)
Try and play with this. If you get stuck because you need to preserve in memory the fact that the user has hit a certain button, know that this is managed by a small gist called SessionState and you can find snippets all around the forum using this gist to preserve state accross Streamlit runs (like here).
Fanilo