Postgresql Function

hi
i want to create a function in postgresql that take input for columns from user and for example first_name , last_name, addres. and will put them into table , and i also want to use exception if user enters wrong data. will some one help me how can i create thats function , because i am new to postgresql . i know how to do it in MS-SQL , i also have that code .if you dont understand what am trying to say . i can post sql code .thanks