How to make a Java constructor for a class that implements an interface

I have an interface I need to use that looks similar to:

public interface Classroom {
    enum Grade {
        Primary, Elementary
    }

    Map<String, String> students();

    String grade();

    Optional<String> teacher();
}

I know in order to use an interface, I need to implement it as a class. However, I don't understand how to create the constructor for the class? I don't have any other methods or variables to add to the interface Classroom, I just need a constructor for it so I can use it and create a Classroom object.

public class BiologyClassroom implements Classroom {
    public BiologyClassroom(Map<String, String> students, String grade, Optional<String> teacher) {
        // not sure what to put here?
    }
}

When I do try to use the interface by doing Classroom classroom = new Classroom() which I know is wrong, my IDE will fix it by by replacing it with:

Classroom classroom = new Classroom() {
            @Override
            public Map<String, String> students() {
                return null;
            }

            @Override
            public Grade grade() {
                return null;
            }

            @Override
            public Optional<String> teacher() {
                return Optional.empty();
            }
        }

I don't know how to interpret this suggestion from my IDE, am I supposed to write methods for students(), grade() etc? I just need to make a Classroom object using my own values for students, grade and teacher.

I am new to Java.

The methods in your interface are actually getters (that don't start with "get"), so if you want to avoid repeating too much code, you can use an abstract class:

public abstract class AbstractClassroom implements Classroom {
    private final Map<String, String> students;
    private final Grade grade;
    private final Optional<String> teacher;

    protected AbstractClassroom(Map<String, String> students, Grade grade, Optional<String> teacher) {
        this.students = students;
        this.grade = grade;
        this.teacher = teacher;
    }

    @Override
    public Map<String, String> students() {
        return students;
    }

    @Override
    public Grade grade() {
        return grade;
    }

    @Override
    public Optional<String> teacher() {
        return teacher;
    }
}

You can then write your class BiologyClassroom as follows:

public class BiologyClassroom extends AbstractClassroom {
    public BiologyClassroom(Map<String, String> students, String grade, Optional<String> teacher) {
        super(students, grade, teacher);
    }
}

You can also consider dropping the interface and use the abstract class instead.

In your interface you have declared students, grades, and teacher as methods.
I believe you are intending to use them as variables.

Just use basic inheritance; there is no need for an interface, per se.

class Classroom {
    enum Grade {
        Primary, Elementary
    }

    Map<String, String> students;
    String grade;
    Optional<String> teacher;

    public Classroom(Map<String, String> students, String grade, Optional<String> teacher) {
        this.students = students;
        this.grade = grade;
        this.teacher = teacher;
    }
}

class BiologyClassroom extends Classroom {
    public BiologyClassroom(Map<String, String> students, String grade, Optional<String> teacher) {
        super(students, grade, teacher);
    }
}

Here is the Java tutorial on inheritance.
Inheritance (The Java™ Tutorials > Learning the Java Language > Interfaces and Inheritance).