This gist shows you how to define public and private method and property, also where to define instance variable.

ClassName.h

//
//  className.h
//  Objective-C exploration
//
//  Created by Greg Xu on 8/30/13.
//  Copyright (c) 2013 Greg Xu. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface ClassName : NSObject {
    
    //instance variables declaration can go here
    NSString *instanceVariable;
    
}

//public properties and methods declaration goes here
@property NSString *publicProperty;
-(void)publicMethod;

@end

ClssName.m

//
//  className.m
//  Objective-C exploration
//
//  Created by Greg Xu on 8/30/13.
//  Copyright (c) 2013 Greg Xu. All rights reserved.
//

#import "ClassName.h"

@interface ClassName () {
    
    //instance variables declaration can also go here
    NSString *anotherInstanceVariable;
    
}

//private properties and methods declaration goes here
@property NSString *privateProperty;
-(void)privateMethod;

@end

@implementation ClassName

-(void)publicMethod{

    self.publicProperty = @"publicProperty";
    self->instanceVariable = @"instanceVariable";
    NSLog(@"publicMethod and %@ and %@",self.publicProperty, self->instanceVariable);
    [self privateMethod];
}


-(void)privateMethod{
    
    self.privateProperty = @"privateProperty";
    self->anotherInstanceVariable = @"anotherInstanceVariable";
    NSLog(@"privateMethod and %@ and %@",self.privateProperty, self->anotherInstanceVariable);
}
@end