First of all. If you don't have the resources to contribute don't. If you need to spend your time on your financial situation or family or whatever, take care of yourself first.

But assuming you do have time then there are various ways that you can contribute.

1. Use the software.
2. Share the software. If you have friends, family or coworkers who could benefit from a particular piece of open source software let them know about it. If you have writing or video making skills you can also help by publishing guides and tutorials.
3. Support other users. Whether they are people you know IRL or people on the forms or issue tracker it is always good to help others.
4. Directly contribute to the project. This depends on the project, if they don't have documentation about how to contribute consider reaching out and asking. Let them know what skills you have and how much time you can offer. Frequently projects are looking for people to provide support to users, write documentation, triage bugs or other tasks. Reaching out also helps make sure that the work you are doing is useful and follows the project's conventions.
5. Specialized contributions. If you have specialized skills like programming, graphic design, UX expertise, speak multiple languages or anything else then the project can often find a use for you. Again, I recommend reaching out first to make sure that the work you do is desired and in the direction that the project wants to go. If you don't have these skills right now it is never too late to learn either. There are many online courses (many free) that can help you learn to program or do design.