Theory

"Difference between class and object" http://www.differencebetween.info/difference-between-object-and-class
"Constructor in Ruby" http://ruby-for-beginners.rubymonstas.org/writing_classes/initializers.html
"Methods in Ruby" https://www.tutorialspoint.com/ruby/ruby_methods.htm

Learn by examples

Class definition
- move to directory examples/1_1_class_definition
```
cd examples/1_1_class_definition
```
- take a look at animal.rb file
- try to use code in irb as described in try_it_yourself.rb file
Constructor and instance vars
- move to directory examples/1_2_constructor_and_vars
```
cd examples/1_2_constructor_and_vars
```
- take a look at animal.rb file
- try to use code in irb as described in try_it_yourself.rb file
Constructor with parameters
- move to directory examples/1_3_class_with_params
```
cd examples/1_3_class_with_params
```
- take a look at animal.rb file
- try to use code in irb as described in try_it_yourself.rb file
Constructor with optional parameters
- move to directory examples/1_4_class_with_optional_params
```
cd examples/1_4_class_with_optional_params
```
- take a look at animal.rb file
- try to use code in irb as described in try_it_yourself.rb file
Method definition
- move to directory examples/1_5_method_definition
```
cd examples/1_5_method_definition
```
- take a look at animal.rb file
- try to use code in irb as described in try_it_yourself.rb file

Learn by experience

Create class Person with:

instance vars: @id, @name, @age
constructor with name and age as parameter (name should be optional [default "Unknown"])
extra method is_of_age? (returns true/false)