ResearchGate has some cooperation with large publishers, and many publications are imported automatically. However, there is no other import function provided directly to users. You may check at https://www.researchgate.net/profile/Ekaterine_Javakhishvili/unconfirmed (visible only to you) whether some of your publications are already at ResearchGate. For these you just have to confirm authorship. I am not sure whether this list of unconfirmed publications is really complete - ResearchGate's algorithm for identifying authors is far from being perfect. You may also search for the titles of your publications at https://www.researchgate.net/search.Search.html?query=&type=publication. For publications not found by one of these ways, you have to create new pages "by hand".