I want to design smaller circuit boards (2x4cm and smaller) and I am looking for a good, reliable, if possible free software for designing PCB.
I haven't done it and am not sure what formats are the best for PCB companies like JLCPCB.
The circuits will use SMD components of various sizes even 0402.
So what software out there do you recommend?
I've found KiCad to be great and easy to use. It is not perfect, but there is a lot of guides on the web to handle most issues.
There are a great many threads on PCB software recommendations on this site, search for them.
I have been using Autodesk Eagle for quite some time and I have gotten some good results from it. The schematic and layout screens are user-friendly, and making your own component symbols and packages couldn't be easier. There is a standard free version and a paid premium version, but students can get the premium version for free.