Swift

let frame = CGRect(x: 0, y: 0, width: 100, height: 100)
let textField = UITextField(frame: frame)

Objective-C

CGRect *frame = CGRectMake(0, 0, 100, 100);
UITextField *textField = [[UITextField alloc] initWithFrame:frame];

Interface Builder

You can also add a UITextField to a storyboard by dragging it from Object Library.