在rails的下拉列表中显示数据库中的数据

I have one table, categories where I have name of category and ID. I have to create a form where I need to show a dropdown box which has a list of categories from table. As I am a beginner in ruby on rails, I dont know how to do that. Please help. Here's my _from.html.erbI have one table, categories where I have name