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An Objective-C class needs an interface (header) and implementation:

#import <Foundation/Foundation.h>

@interface Point : NSObject
@property int x;
@property int y;
- (double)distanceFrom:(Point *)other;
@end

@implementation Point
- (double)distanceFrom:(Point *)other {
    int dx = self.x - other.x;
    int dy = self.y - other.y;
    return sqrt(dx * dx + dy * dy);
}
@end

• @interface ClassName : Superclass — declares the class
• @property — auto-synthesizes getter/setter
• - (returnType)methodName... — instance method (the -)
• + (returnType)methodName... — class method (the +)
• @end closes the block
• self is the receiver inside a method (like this)

Creating instances:

Point *p = [[Point alloc] init];
p.x = 3;
p.y = 4;

The [Class alloc] allocates memory; init initializes. Modern code may use [Class new] which combines them.