General question: How to write a script to open and add input to a website? [closed]

I have a work, where I have to create data over our intern website. Its really much input I always have to put in. It took us hours... Now i want to write a code, where the script should open a website. After it opened it successfully, it should put some input values on a textfield of the Webseite and after the input it should click a button to submit the input.

I have never worked in that direction, so I have really no glue. Could you guys give me some starting help? Which programming language is most suitable? Which websites are good to learn for something like this. Videos? How are your experience with that topic? If there are similar questions on stack overflow, please send it.

Guys I am really happy with all small inputs you can give me. I need a direction to start my search.

Many thanks in advance.