UICollectionView - distance between cells?

You can configure spacing between cells or rows by using following properties.
1) For setting space between rows.

[self.collectionView setMinimumLineSpacing:5];

2) For setting space between items/cells.

[self.collectionView setMinimumInteritemSpacing:5];

You can also configure it from InterfaceBuilder(IB). Just select UICollectionView from storyboard/Xib file and click in Size Inspector as specified in below image.

From this. You need to change minimumInteritemSpacing and minimumLineSpacing.

UICollectionViewFlowLayout *flow = [[UICollectionViewFlowLayout alloc] init];
flow.itemSize = CGSizeMake(cellWidth, cellHeight);
flow.scrollDirection = UICollectionViewScrollDirectionHorizontal;
flow.minimumInteritemSpacing = 0;
flow.minimumLineSpacing = 0;
mainCollectionView.collectionViewLayout = flow;

This UICollectionViewFlowLayoutDelegate method will help you..

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionView *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section  
  {
    return 10; // This is the minimum inter item spacing, can be more
  }

One more if you need more space to arrange your cells adjust the edgeInsets also

No, it doesn't. Just change the layout's minimumInteritemSpacing.