a!StartProcess and a!StartProcessLink

Please find all details you are looking for on this documentation page https://docs.appian.com/suite/help/22.1/Ways_to_Start_a_Process_From_a_Process.html#starting-a-process-from-an-interface

It shows a full comparison of all ways to start a process.

In simple words "a!startProcess" is a function and it can only execute inside a saveInto or a Web API on the other hand in "a!startProcessLink" users are shown the start form or first chained attended node and any subsequent chained forms. After submitting the last form, the chain completes, the user returns to the original interface, and that interface reloads. I hope that explanation will give you brief idea.

you can learn more about them from https://docs.appian.com/suite/help/22.1/Ways_to_Start_a_Process_From_a_Process.html

Thanks

Thanks 

Thanks

Thanks for the Answer

what is mean by custom banner on submit button

in Start Process link you can see the parameter Banner Message  needs to provide the custom message to display once after the process completes.

https://docs.appian.com/suite/help/23.4/alert-banners.html

Displays banner message like this after process gets completed. Used for Readability purpose   

I don't find it useful at all. Because even if you click on cancel, it will still show the same banner. To be honest, this is completely useless unless you only have a way forward and cannot cancel or go back.