I recently had to transition to a web team from an API team at work. It was a difficult transition, but overall, it's a transition that I am really happy about. I like the new team and the new learning opportunities transitioning to a new team allows me. I bet starting a new job probably results in a similar situation, but with a bigger scope of new work to learn about. Here are some tips for someone who's starting a new job or transitioning to a work that will help you to get use to the new tasks as a software engineer.
1. Learn the directory structure of the codebase
Learning 100% of the codebase in a short period of time is difficult. This can be made easier by having someone explain the directory structure of the codebase for you. Once you understand the context of the directory sturcture, smaller parts of the codebase can be made more sense easier.
2. Ask questions to the teammembers
You have the experts of the codebase sitting around you. Ask them questions and get the answers you need. Have the questions be about things that you can't figure out on your own. For example, questions about codebase can be figured out on your own with some struggles, but questions about how Akamai cache is set up, how deployment works, how testing works, how oncall process works, etc can't be figured out on your own. So for these things, you have ask questions.
3. Have a vision
You should have a vision for your own work aside from the day to day work at the team. This was a better advice I've received from a coworker, and he is right. Doing your day to day job well makes you a good engineer. If you have a vision about the project you work on and attempt to improve the product with a vision, you can be a great engineer. You have to ensure that your vision is aligned with the product vision, team vision and the company vision.