Which open source projects are you using and you like? Try to contribute to them.
Start sending bug reports that are very useful and dometimes underestimated. Look how/where they fix them and the next time try to send a pull request (or another bug report).
Fixing typos in docs is also a good starting point.
If you want to send a new feature, start with something small, like a weekend project. You never know if the mantainer will like it, or if they are morons or if they have very weird code rules.
I am in webapp development using react and node js. So currently I am looking towards the good first issues of the some repositories to make myself comfortable with the repository environment. But most of the repos don't hold these good first issues...So I am confused
I don't like "good fist issues". The real good first issues are so small that it's easier to fix them than labeling them as "good first issues".
If you find something that is labeled with "good first issue", it's probably a weekend project, where you have to make a few modifications and add test and tweeks.
Start with something smaller.
(If you are use to github actions, you can try to transform the manual test in the repos to automatictests. my guess is that react and node.js already have them, but there may be some related side projects that still have manual tests.)
Start sending bug reports that are very useful and dometimes underestimated. Look how/where they fix them and the next time try to send a pull request (or another bug report).
Fixing typos in docs is also a good starting point.
If you want to send a new feature, start with something small, like a weekend project. You never know if the mantainer will like it, or if they are morons or if they have very weird code rules.