Calling one Activity from another in Android

How can I call another activity from one (the current) activity?

And for the same I want to call an activity which contains a dialog message box from my current activity.

First question:

Use the Intent to call another Activity. In the Manifest, you should add

<activity android:name="ListViewImage"></activity>
<activity android:name="com.company.listview.ListViewImage">
</activity>

And in your current activity,

btListe = (ImageButton)findViewById(R.id.Button_Liste);
    btListe.setOnClickListener(new OnClickListener()
    {    public void onClick(View v)
        {
            intent = new Intent(main.this, ListViewImage.class);
            startActivity(intent);
            finish();
        }
    });

Second question:

sendButton.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            String valueString = editValue.getText().toString();
            long value;
            if (valueString != null) {
                value = Long.parseLong(valueString);
            }
            else {
                value = 0;
            }

            Bundle sendBundle = new Bundle();
            sendBundle.putLong("value", value);

            Intent i = new Intent(Activity1.this, Activity2.class);
            i.putExtras(sendBundle);
            startActivity(i);

            finish();
        }
    });

and in Activity2:

 Bundle receiveBundle = this.getIntent().getExtras();
    final long receiveValue = receiveBundle.getLong("value");
    receiveValueEdit.setText(String.valueOf(receiveValue));
    callReceiverButton.setOnClickListener(new OnClickListener() {
        public void onClick(View v) {
            Intent i = new Intent(Activity2.this, Receiver.class);
            i.putExtra("new value", receiveValue - 10);
        }
    });

check the following code to call one activity from another.

Intent intent = new Intent(CurrentActivity.this, OtherActivity.class);
CurrentActivity.this.startActivity(intent);

I used following code on my sample application to start new activity.

Button next = (Button) findViewById(R.id.TEST);
next.setOnClickListener(new View.OnClickListener() {
    public void onClick(View view) {
        Intent myIntent = new Intent( view.getContext(), MyActivity.class);
        startActivityForResult(myIntent, 0);
    }
});