You can use JetBrains AI Assistant to summarise one or more commits from the Git (or other VCS) tool window. Open the tool window with ⌘9 (macOS) / Alt+9 (Windows/Linux) and select one more commits that you would like to ask AI Assistant for help with.

Right-click in the Git tool window and select Explain Commits with AI Assistant. The AI Assistant tool window will open and generate an answer that summarises the commits you selected. This can be really helpful when you want to get a summary of someone else's commits, or you can't remember your own!