It's normal to be nervous when starting a new job -- especially one with a different set of responsibilities -- but it's also exciting! Think of it as an opportunity to learn and grow.
I'm assuming you have some background in coding and have written code before. Just remember that even the most complex, daunting programs and processes all start from the same building blocks as a 'Hello World' program. Most are also broken down into smaller logical pieces.
I think one of the best ways to get started is to look at the code that already exists. Does your company use a source control tool like GitHub? If so, a good first step would be to get access to the main repo and start reading the existing codebase. Try thinking of something the program or service does and tracing it through the code. Make sure you understand what commonly used shared functions/utils do.
Starting with bugs, like shabunc recommended, is a good idea. Another way to start is to ask if there are any small, discrete features on the roadmap, and see if you can figure out how to implement them.
Some advice if you're truly brand new to coding: start by looking at the problem and writing down what features or functions have to be part of a minimal viable solution to the problem. Then think about how to make these functions work logically -- basically, psuedocode a high-level solution. Finally, sit down and try to write it, testing individual functions as you go. Breaking it down into pieces can make the process less daunting.
There are lots of online resources for coding, depending on what you're developing and what language you're using. And remember: pretty much every programmer spends a lot of their time googling syntax, error codes, and problem solutions; no one knows everything going in.
Coming from someone who recently shifted from a largely non-technical role to a largely technical role, it's definitely possible -- and fun. Best of luck!