If you are a beginner, then the first thing you should be doing after creating your account is exploring this website.I would recommend upgrading to premium account as it unlocks better features than a normal account. You will get better experience with a premium account along with more unlocked courses and questions by different companies.
First step would be to explore the website. Just check the different pages of Explore, Problems, Mock, Contest, Articles, Discuss,etc. Check out what content these pages have. This will make you familiar to this awesome coding platform. :)
Second, if you know basics of any programming language, you can go to the Problems Section https://leetcode.com/problemset/all/ .It contains almost every type of coding problems that can be asked you in a technical interview. Another option is to start learning a Computer Science topic from the Explore Section []https://leetcode.com/explore/.
Third, after some warmup problems, checkout the Articles Section (https://leetcode.com/articles/) and Discuss Section (https://leetcode.com/discuss/). The articles might have explanations about a particular topic or some useful tips and tricks in programming. Make sure, to check them out regularly, as you may need the concepts at some point. In the discuss section, different LeetCode users post their problems, questions, answers, etc. So, even this section will help you in driving your mind in the right direction while solving a problem or in programming. It'll help you to train your mind about how to write a robust code.
You also have a Playground section which is very helpful for running your code or testing some modules. It is just an environment in which you can test custom code that you type in, the language you prefer.
That's it ! Hope you liked my post. Happy Coding ! : )