You may be here because you are starting your email automation and you have seen this screen below after you clicked Create New Automation.
You may be asking yourself now, what is the difference between "On Subscribe" and "List Name"
I'm going to break that down for you right now.
On subscribe is going to be useful when you are bringing in leads either through an Emercury Web form or through a live API feed from a form on your website. So when a lead comes into your list the first message can be sent based on that added time.
On List Name can be used if you already have an existing with subscribers on it and you want to start an email automation from today with all these subscribers and then anyone added after today will then be added to the automation schedule. This means the first email will go out in bulk but your secondary emails can be dripped based on what your triggers are in the rest of your workflow. If the trigger is based on opens or clicks then it will be drip the rest of the way. If the condition is only based on days then this will be sent based in full each day.
So the big difference is starting from day 1 with new subscribers "On Subscribe" and starting with an pre-existing list that you you are starting a new automation with.