My toddler always needs me and crys when She goes to preschool. What do I do

This is just seperation anxiety.  You will have to start walking away and letting her cry.  It's tough but, she will learn that you are coming back.  Ask the preschool teachers for some help.

This is normal for children. Separation anxiety. Talk to the teachers and let them know that you need their help getting her to feel comfortable. Ask them if they will allow you to bring in pictures that she can have in the room of you if that will help her. Also when you bring her in the teachers should make her feel welcome by saying hi and coming over to her. This is when you should put her stuff away for the day if she has a cubby and let her know you love her and will see her later. She might cry but believe me hug her, say goodbye and hand her to a teacher then go. THe longer you hang around the harder it will be for her. You can call the center later on and ask to speak with the teacher and they will tell you how shes doing.