Help i have a few questions about health!?

Ok so i am 11 fixing to turn 12 in august.. I start middle school the day before my birthday.. which is august 3rd.. I am nervous about my period.. I started thinking about it the other night before bed and had a dream about it... (not very pleasant) My back aches.. My breats hurt.. and like on my panties it looks like its been wet tworad the top not bottom.. not pee ( i dont leak) and is it sweat? I am nervous about telling my mom but ill knwo i ahve to.. soo when i get pads how do you use them??? I am nervous that in middle school ill leak in the chair of my seat!! How would that happen wouldnt the pad catch the blood??? And when im sleep i am scared when i wake up that there will be blood in my bed or when im traveling ims cared there will be blood in the chair!! Help cuz this worries me deeply!!!