How to understand the principle of calculating the h-index on researchgate? Where at researchgate can I see which article has been cited and how many times? I didn't find it in the help.
The h-index is calculated automatically from the identified citations, and these identifications are also made automatically. Unfortunately, for various reasons the identification of citations is very often incomplete in ResearchGate, and it is not possible to add citations "by hand". See also the help page https://help.researchgate.net/hc/en-us/articles/14295647367697-h-index. You will find statistics of the citations in https://www.researchgate.net/profile/Boris-Klimenkov/stats/citations.
Regarding your question how to find the citations details you have to click on the individual paper link here on RG and you find the citation number and the detailed info about which papers cited your work.
Regarding the h-index you need to understand that although your most cited paper (go to stats and scroll down)
Article Microstructure and Magnetic State of Fe3O4-SiO2 Colloidal Particles
is cited 22 times, the h-index is defined as the number of papers that are cited at least the same times. In your case apparently 3 papers are at least cited here on RG 3 times, therefor your h-index is 3.
Best regards.
PS. In Google scholar your h-index is 5 (although according to the definition it should be 6). In most cases the number of citations in GS is higher than in RG (this has as indicated by Wolfgang R. Dick various reasons).
Take for example Article Porous silicon and graphene-based nanostructures for novel s...
this work cites one of your conference papers but the reference to your conference paper is not recognised by the search engine/algorithm of RG (click on references).