Hi, im a 19 year old girl that is bisexual and i need help finding myself&knowing da tips when a girl likes me?

Well lately I haven't been my self I'm lost, I'm becoming a women and im realizing im more attractive to women, I want to have the guts to ask a girl out but how do I knw if that girl likes girl? I heard about the thumb ring & purple thread string mayb ill try that. Well im getting older and want that sexual experience its killing me. The problem is im so girlly n I think dats y any girls hit on me. There's this one girl I like in class she sits in front on me. The first time I saw her she caught my eyes and every time she sit dwn in class we do I contact but in serious way no smiles I feel this fire this weired sense dat she feels the same way. She look geeky n nerdy but I like dat . One day when class was over n we was heading out she was in front of me but I was little behind I thought she was going to close the door bcus I was really far behind so she looked back and she saw me so she holded the door and went Around it until I came so when I came she smiled at me first like an AWEE monemt so I said awe so nice thank you in that instint I told myself why would she do that she was already out the door and I wasent even near? Please help me.