shaharom - I'm assuming that you don't have an experienced flyer handy to ask these questions or help you at the field. Sit down at home and just play with your plane and the transmitter trims and see what effect they have on the plane. Become familiar with all of this without making any permanent changes for now. Take someone, anyone handy, to the field with you. Discuss briefly with them how the trim controls work and explain which controls do what until they understand it in the same manner as you. Once in the air, YOU fly the plane and ask them to move the trim levers for you so that you will not be distracted by needing to look away from the plane. Have them move the appropriate trim in response to your request in small amounts (a couple of clicks) per correction so as not to over correct. The MOST important thing to do is FLY THE PLANE, worry about the trim second and altitude is your friend (up to a limit) as it gives you time to correct for mistakes.
Welcome to RC flying and I hope all goes well for you. We have a number of RCU members from your country and although it is a very large country you should be able to find someone to fly with and help. Ask at your local hobby shop (LHS).