can anyone tell me how to make a character jump in a FPS game?

Questions & Answers
1

using UnityEngine;
using System.Collections;

// basic WASD-style movement control
// commented out line demonstrates that transform.Translate instead of charController.Move doesn't have collision detection

[RequireComponent(typeof(CharacterController))]
[AddComponentMenu("Control Script/FPS Input")]
public class FPSInput : MonoBehaviour
{
    public float speed = 6.0f;
    public float gravity = -9.8f;
    public float jumpSpeed = 8.0f;

    private CharacterController _charController;
    private Vector3 moveDirection = Vector3.zero;
    private bool grounded = false;

    void Start()
    {
        _charController = GetComponent<CharacterController>();
    }

    private void FixedUpdate()
    {
        if (grounded)
            //we are grounded, So recalculate moved direction directly from axes
            if (Input.GetButton("jump")) moveDirection.y = jumpSpeed;
    }

    void Update()
    {
        //transform.Translate(Input.GetAxis("Horizontal") * speed * Time.deltaTime, 0, Input.GetAxis("Vertical") * speed * Time.deltaTime);

        float deltaX = Input.GetAxis("Horizontal") * speed;
        float deltaZ = Input.GetAxis("Vertical") * speed;
        Vector3 movement = new Vector3(deltaX, 0, deltaZ);
        movement = Vector3.ClampMagnitude(movement, speed);

        movement.y = gravity;

        movement *= Time.deltaTime;
        movement = transform.TransformDirection(movement);
        _charController.Move(movement);
    }
}
2

From my comment on the main post. Try adding the jump to Update, and applying the value to movement.y

using UnityEngine;
using System.Collections;
       
// basic WASD-style movement control
// commented out line demonstrates that transform.Translate instead of charController.Move doesn't have collision detection
       
[RequireComponent(typeof(CharacterController))]
[AddComponentMenu("Control Script/FPS Input")]
public class FPSInput : MonoBehaviour
{
    public float speed = 6.0f;
    public float gravity = -9.8f;
    public float jumpSpeed = 8.0f;

    private CharacterController _charController;
    private Vector3 moveDirection = Vector3.zero;
    private Vector3 movement = Vector3.zero;
    private bool grounded = false;

    void Start()
    {
        _charController = GetComponent<CharacterController>();
    }

    //FixedUpdate removed.

    void Update()
    {
        //transform.Translate(Input.GetAxis("Horizontal") * speed * Time.deltaTime, 0, Input.GetAxis("Vertical") * speed * Time.deltaTime);

        float deltaX = Input.GetAxis("Horizontal") * speed;
        float deltaZ = Input.GetAxis("Vertical") * speed;

        movement = new Vector3(deltaX, movement.y, deltaZ);

        if (grounded)
            //we are grounded, So recalculate moved direction directly from axes
            if (Input.GetButton("jump"))
                movement.y = jumpSpeed;

        // Not needed as x/y will always be less then speed unless a frame is greater then one second, as the input value is  always 0-1.
        // movement = Vector3.ClampMagnitude(movement, speed);

        movement.y = Mathf.Clamp(movement.y + gravity * Time.delatTime, gravity, float.PositiveInfinity);

        movement.x *= Time.deltaTime;
        movement.z *= Time.deltaTime;
        movement = transform.TransformDirection(movement);
        _charController.Move(movement);
    }
}

Note had to make movement a class variable so the y value would keep through frames, and also apply gravity over time so the jump speed would decrease over time, letting the player fall.