Collection view cells and headings which, together, give a nice grid with light gray borders between each element.

FDRCollectionViewCell.h

//
//  FDRCollectionViewCell.h
//  
//
//  Created by Brent Royal-Gordon on 7/10/13.
//
//

#import <UIKit/UIKit.h>

@interface FDRCollectionViewCell : UICollectionViewCell

@end

FDRCollectionViewCell.m

//
//  FDRCollectionViewCell.m
//  
//
//  Created by Brent Royal-Gordon on 7/10/13.
//
//

#import "FDRCollectionViewCell.h"
#import "FDRCollectionViewFlowLayout.h"

@interface FDRCollectionViewCellBackgroundView : UIView

@property (assign, nonatomic) BOOL rightBorderHidden;
@property (assign, nonatomic) BOOL bottomBorderHidden;

@end

@implementation FDRCollectionViewCell

- (void)awakeFromNib {
    [super awakeFromNib];
    
    self.backgroundView = [FDRCollectionViewCellBackgroundView new];
    self.backgroundView.backgroundColor = self.backgroundColor;
    self.backgroundView.opaque = self.opaque;
    
    self.selectedBackgroundView = [UIView new];
    self.selectedBackgroundView.backgroundColor = [UIColor colorWithWhite:0.0 alpha:0.03];
    self.selectedBackgroundView.opaque = NO;
}

- (void)setBackgroundColor:(UIColor *)backgroundColor {
    super.backgroundColor = backgroundColor;
    
    self.backgroundView.backgroundColor = backgroundColor;
}

- (void)setOpaque:(BOOL)opaque {
    super.opaque = opaque;
    
    self.backgroundView.opaque = opaque;
}

- (void)applyLayoutAttributes:(FDRCollectionViewLayoutAttributes *)layoutAttributes {
    [super applyLayoutAttributes:layoutAttributes];
    
    FDRCollectionViewCellBackgroundView * background = (id)self.backgroundView;
    background.bottomBorderHidden = layoutAttributes.inLastRowOfSection && !layoutAttributes.inLastSection;
    background.rightBorderHidden = layoutAttributes.againstRightEdge;
}

@end

@implementation FDRCollectionViewCellBackgroundView

- (void)setBottomBorderHidden:(BOOL)bottomBorderHidden {
    _bottomBorderHidden = bottomBorderHidden;
    [self setNeedsDisplay];
}

- (void)setRightBorderHidden:(BOOL)rightBorderHidden {
    _rightBorderHidden = rightBorderHidden;
    [self setNeedsDisplay];
}

- (void)drawRect:(CGRect)rect {
    [super drawRect:rect];
    
    [[UIColor colorWithWhite:0.74 alpha:1.0] set];
    
    CGFloat thickness = 1 / self.contentScaleFactor;
    
    if(!self.rightBorderHidden) {
        UIRectFill(CGRectMake(CGRectGetMaxX(self.bounds) - thickness, 0, thickness, CGRectGetHeight(self.bounds)));
    }
    if(!self.bottomBorderHidden) {
        UIRectFill(CGRectMake(0, CGRectGetMaxY(self.bounds) - thickness, CGRectGetWidth(self.bounds), thickness));
    }
}

@end

FDRCollectionViewFlowLayout.h

//
//  FDRCollectionViewFlowLayout.h
//  Feeder
//
//  Created by Brent Royal-Gordon on 7/11/13.
//  Copyright (c) 2013 Architechies. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface FDRCollectionViewFlowLayout : UICollectionViewFlowLayout

@end

@interface FDRCollectionViewLayoutAttributes : UICollectionViewLayoutAttributes

@property (assign, nonatomic, getter = isInLastRowOfSection) BOOL inLastRowOfSection;
@property (assign, nonatomic, getter = isInLastSection) BOOL inLastSection;

@property (assign, nonatomic, getter = isAgainstRightEdge) BOOL againstRightEdge;

@end

FDRCollectionViewFlowLayout.m

//
//  FDRCollectionViewFlowLayout.m
//  Feeder
//
//  Created by Brent Royal-Gordon on 7/11/13.
//  Copyright (c) 2013 Architechies. All rights reserved.
//

#import "FDRCollectionViewFlowLayout.h"

@implementation FDRCollectionViewFlowLayout

+ (Class)layoutAttributesClass {
    return [FDRCollectionViewLayoutAttributes class];
}

- (void)intuitSectioningAttributes:(FDRCollectionViewLayoutAttributes*)attributes {
    NSIndexPath * lastIndexPath = [NSIndexPath indexPathForItem:[self.collectionView numberOfItemsInSection:attributes.indexPath.section] - 1 inSection:attributes.indexPath.section];
    attributes.inLastRowOfSection = [lastIndexPath isEqual:attributes.indexPath] || attributes.center.y == [super layoutAttributesForItemAtIndexPath:lastIndexPath].center.y;
    
    attributes.inLastSection = attributes.indexPath.section == self.collectionView.numberOfSections - 1;
    
    attributes.againstRightEdge = CGRectGetMaxX(attributes.frame) == CGRectGetMaxX(self.collectionView.bounds);
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
    FDRCollectionViewLayoutAttributes * attributes = (id)[super layoutAttributesForItemAtIndexPath:indexPath];
    
    [self intuitSectioningAttributes:attributes];
    
    return attributes;
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
    NSArray * attributesArray = [super layoutAttributesForElementsInRect:rect];
    for(FDRCollectionViewLayoutAttributes * attrs in attributesArray) {
        [self intuitSectioningAttributes:attrs];
    }
    return attributesArray;
}

@end

@implementation FDRCollectionViewLayoutAttributes

- (id)copyWithZone:(NSZone *)zone {
    FDRCollectionViewLayoutAttributes * copy = [super copyWithZone:zone];
    
    copy.inLastRowOfSection = self.inLastRowOfSection;
    copy.inLastSection = self.inLastSection;
    
    copy.againstRightEdge = self.againstRightEdge;
    
    return copy;
}

@end

FDRSectionHeaderView.h

//
//  FDRSectionHeaderView.h
//  Feeder
//
//  Created by Brent Royal-Gordon on 7/11/13.
//  Copyright (c) 2013 Architechies. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface FDRSectionHeaderView : UICollectionReusableView

@property (weak, nonatomic) IBOutlet UILabel * titleLabel;

@end

FDRSectionHeaderView.m

//
//  FDRSectionHeaderView.m
//  Feeder
//
//  Created by Brent Royal-Gordon on 7/11/13.
//  Copyright (c) 2013 Architechies. All rights reserved.
//

#import "FDRSectionHeaderView.h"

@implementation FDRSectionHeaderView

- (void)drawRect:(CGRect)rect {
    [super drawRect:rect];
    
    [[UIColor colorWithWhite:0.74 alpha:1.0] set];
    
    CGFloat thickness = 1 / self.contentScaleFactor;
    
    UIRectFill(CGRectMake(0, 0, CGRectGetWidth(self.bounds), thickness));
    UIRectFill(CGRectMake(0, CGRectGetMaxY(self.bounds) - thickness, CGRectGetWidth(self.bounds), thickness));
}

@end

Hi am two months of experience in ios. i don't know how to use those classes. so please explain briefly