If a girl sits next to you what does it mean?

It's often soft signs. Kissing will not happen if you two are not already in a relationship with eachother. Usually, it's little things such as playing with her hair (which happens more often than most girls will admit. It's like a natural or nervous tick we have), softly figiting or tangling her fingers, making a point of poking or touching your arm or shoulder when getting your attention or talking to you, mild giggling, frequent glances towards you, blushing if you give her compliments or talk to her. Little things. The list goes on. General flirting. Don't worry. It takes a while to really recognize flirting for what it really is. ;)