How to implement repository pattern in asp.net core 2.1

Question

Problem

How to implement repository pattern in asp.net core 2.1 visual studio 2017 with SQL server 2012 ?

i work on project work on repository pattern but i cannot implement it

model Employee

public class Employee
{
public int EmployeeId { get; set; }
public int BranchCode { get; set; }
public string EmployeeName { get; set; }
public int EmployeeAge { get; set; }
}
Repository public class RepositoryTab : IrepositoryTab where T : class
{
protected TabDbContext db { get; set; }
private DbSet dbSet;
 public RepositoryTab(TabDbContext Tabdb)
{
 db = Tabdb;
 dbSet = db.Set();
}
public IEnumerable GetAll()
{
 return dbSet.ToList();
 }
}
public interface IrepositoryTab where T : class { IEnumerable GetAll();
T GetById(object Id);
 }

 1- How to define repository on controller Employee to call function GetAll on constructor?

meaning how to define repository on constructor of controller

3- suppose i have compost key how to use getbyid suppose i have (Employeid,branchcode) as compost key ?

are compost key define as fluent api or annotation or what ?

please can you help me and give me details if possible

can any one answer me of this question please ?