Hello Friends,
NSMutableAttributedString allows to set different attributes(font size,font color) for different parts of the string.
To use NSMutableString you may use the following code:
//Create an object of NSMutableAttrinbuteString and assign it with the complete string

NSMutableAttributedString *stringToSet = [[NSMutableAttributedString alloc]initWithString:@"your string goes here"];

//To set different font Color

[stringToSet addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:NSMakeRange(0,10)]; //User Defined Range
    [stringToSet addAttribute:NSForegroundColorAttributeName value:[UIColor blueColor] range:NSMakeRange(10,20)]; // User Defined Range

//To set different font Style  


 [stringToSet addAttribute:NSFontAttributeName value: [UIFont fontWithName:@"Roboto-Regular" size:15.0] range:NSMakeRange(0,10)];
    [stringToSet addAttribute:NSFontAttributeName value:[UIFont fontWithName:@"Roboto-Light" size:14.0] range:NSMakeRange(10,20)];

To set this attributed string on label you will have to use attributedText property of label and set as follows: userLbl.setAttributedText = stringToSet;