You need to first learn Java (Basic). If not, then selenium is available in many other programming language bindings. you can choose the language which you are comfortable with.
As far as errors are concerned:
1. static variable "error" is declared as String and it does not have a get method.
2. assert_login method accepts an object of type WeDriver and you are passing and object of type boolean. so that won't work.
A quick search on google for page objec model in selenium returned below results:
You can look for other tutorials too.