While you are not restricted to using JavaScript in TestComplete, in addition to LinoTadros and his immensely helpful information (I learned a lot from him as well, back in the day) might I suggest engaging in an online tutorial for learning coding? Check out https://www.w3schools.com/js/default.asp
While you aren't going to be writing application level code, something like this is helpful for the following reasons:
1) Learning how code works and is written and is built makes you a better tester over all as it will help you better understand how the application works and, therefore, how best to test things.
2) Even if you write only Keyword based tests in the visual editor, you will still need to understand things like variables, parameters, data types, if-then, loops, etc. Programming logic is part of any good automated test because there will always be conditions that you'll need to write logic to account for
3) While keyword tests in TestComplete have come a long way, I still find that sometimes the most elegant way to perform certain tasks and checks is in code and not in keyword tests. You will, eventually, find yourself needing to write something that will be easier to do in script code.
Happy testing!