Save last user input action is a good way to collect and store data from your customers, as well as re-use user responses in a conversation.

Once you click on the "Save last user input" option, you will be asked to write down a name for the Variable. 

In the example below, the name of the variable is: Favorite-bot-company. The text component above the Action asks users for the input - "what is your favourite chatbot company?"

The last user input will be saved as a variable that you can re-use in other parts of your bot, as shown in screenshot below. 

The format for using a pre-defined variable in the chatbot is: ${Variable_Name}

If you save another user input into the same variable, the original user input will be overwritten.