How Can I insert the username of who submitted a form to the database?

[EquinoxWorld]

Hello everyone, I am trying to capture the username of whoever submits a custom form I created. I need to insert that username of who submits the form into a database table I created. I need this to first have a record of who submitted the form and also to later print out the username next to the form submitted, as well as restrict later access to that form using if conditions, but first I need to get that username. Any one has any ideas how to go about this or point me in the right direction?? Please any information would be very useful. Thank you for your time everyone.