It is called masturbation. Person gets sexual pleasure and some satisfaction out of the act. There is nothing wrong about it. It is natural (physiological) urge, both male and female will have. Females are using different objects to get stimulation. Objects vary from what you described to vibrators and artificial penis. Insertion of objects requires caution so that one would not cause injury to soft skin of genitalia (sex organ). You need to control your urge only in case of compulsion. (Means if you do not masturbate then you become restless and compulsorily you have to masturbate to feel relaxed). Otherwise, it is much better then having unsafe sex or sex with an irresponsible partner.
It is nice to know that you are discussing such issues with your mother. We should always give proper sex education to our children so that they can emerge as sexually healthy adults.