Contributing can be daunting at first, but this is the first step of a rewarding journey, using your experience to benefit others while learning and meeting new passionate people.
Every project is different
Every project is different, so don't hesitate to look at multiple initiatives to find what makes the most sense to you. Look at their project page and website, issues tagged "goodfirstissue", and contact them if you have any questions.
To have a better idea of how the team works and how to help, you can also check the contribution guidelines and past pull requests.
You don't need to be an expert, all support matters
Depending on your goals and expertise, you may very well find yourself outside of your comfort zone. This is perfectly normal, and part of the learning experience. As long as you are motivated to learn and help, maintainers of open source projects are usually happy to help and guide you, to have your contribution integrated.
Contributing to the code base is also one of many ways to help: some need support translating, improving documentation or tutorials, reviewing, or using it. And the simple act of sharing a project with others is also a great way to help.