Text box character limitations and data check?

Hi, everyone. Is there a way to create a text box and let the user enter a maximum of 300 characters in the text box? I also want to check that the user is entering data in the text box. In other words, if the user wants to continue and clicks the submit button without logging in to the text box, I want to warn the user if no any data is entered into the text box, please write something into text box. I want to design this as a stage of a data collection application. How can I do that? Thank you in advance for your help.

I can't answer all your questions. But the place to start would be looking up "inkey" in the manual.