Well this girl moved next door to me but I don't know how to tell her I like her. Cause I don't know how she would react. And I kind of scard of rejectsion so what do I do

Talk to her in a neighborly way, and get to know her, and let her know you. Only then can you even think about anything more. You don't really think she will fall for you, without seeing what kind of guy you are, do you?

Don't tell her you like her. She is your neighbor and you will see her daily.
Talk to her as much as you can without being intrusive. Borrow sugar, lend sugar .
Be helpful if you see her carrying something heavy. Be very neighborly .
After a time invite her over or out . When you live that close , if something is supposed to
Happen it just will.

You could talk to her and try to create opportunities to spend time with her. Don't be afraid of being rejected. Life is short. If you miss someone due to shyness, you would miss her the whole life. Every thing has a destined result for itself.
Come on:)

Talk about anything...
If she smiles, that's good.
If she keeps smiling and asks you questions
If she touches your arm that's the bell, ask her out. (she may not always do that)
If she is polite but doesn't make you feel like asking her out... don't. If she wants you to, she will work to make you relax - then go for it... "Hey, wanna catch dinner at that new restaurant nearby. it looks good..." Bingo.

Invite her over for a movie night. Keep it casual, get some pizza or have some pie. Or offer her the cliché of showing her the neighborhood, provided you have an interesting one to show. You'll know in that first time you hang out if she's A. interested in you and B. if she's interesting enough to you.