I have used entities node. The type is static list and have defined fixed options. Based on the option that user selects the bot should start respective flow.
Can some help me with steps or documentation for this?
You may use an advanced JS template for any message node to display a menu.
One of the popular formats is Button Template
The payload of the button template is what actually goes back to the bot when you click a button. You will need to train the bot (tasks) with the required ML/ pattern as required to make the bot understand and respond to various button clicks.
Some users also use the Entity node static list of values (You may have used it). You will need to use transitions and refer to how to work with entity nodes.