Dan67, you've posted this question in the Find And Run Robot forum section so I assume you want to do this using that program.
You can create an alias with multiple commands that first loads a website in the default browser, then waits a little and then sends keyboard input to the window that was active before FARR was opened. Here is sample code for the results editbox for the alias.
website login | https:://www.google.com ;;; sleep 1000 ;;; sendkeys user name here{TAB}password here{ENTER}
Note that this simple example assumes several things:
1. That the form field you want to input text to automatically has focus when the webpage is loaded. If not then you need to first send {TAB} commands until the form field has focus. On some websites even that might not work and then you'd have to find some other solution.
2. That the webpage is designed in such a way that you can also send {TAB} to navigate from the username field to the password field. Might not always be the case.
3. That you're ok with saving the login credentials in plaintext in a FARR alias. May not be a good idea in some cases, depending on who else has access to the computer, how important the account is and so on. There are various password manager tools that either come with a browser plugin or work as external tools. I suggest you first check if one of them can do what you want.
4. That you can reliably predict how long time the website takes to load each time. 1 second in my example may be too short, at least sometimes.
5. The example method might also be unreliable in a risky way since FARR does not verify that the webpage it is sending the credentials to is really the one that you intended. For example imagine that you during the 1 second (or however long you set it) wait period by mistake switch tab in the browser. FARR won't know that and will send the username and password to whatever website in the new active tab. That could end badly if for example that tab was a live chat.