It's time to do the group activity.

I'll let you know how to do the activity. Leader, I will give you pictures. You should put the pictures face down on the table. Do not let your members see the pictures. You should pick up a picture and show the picture step by step so that the members can guess what he or she is doing. First, cover the picture. And then uncover it step by step. The other members should ask questions beginning "Is he-? or Is she- ? in the present continuous tense."
I'll distribute the pictures to each of you. Take these pictures, and put them facedown on the table. Ready? Let's begin..... Are you finished? OK. Let's stop doing the activity. Listen to me.
-------------------------------
I have written down a group activity, would you check the expressions?

It would be better to say "little by little" rather than "step by step" -- in both places.

In the third sentence, it would be better to say "... so that the members can guess what the person in the picture is doing."

Punctuation corrections:
"Is he-?" or "Is she- ?" in the present continuous tense.

Sure, I can help you check the expressions for the group activity. Here are the phrases and expressions used in the activity:

1. "I'll let you know how to do the activity." - This phrase is a polite way of informing others that you will explain the activity to them.

2. "Leader, I will give you pictures." - This sentence establishes that the leader will be responsible for distributing and presenting the pictures.

3. "Put the pictures face down on the table." - This is a clear instruction for everyone to place their pictures with the image side facing the table.

4. "Do not let your members see the pictures." - This reminds the leader to ensure that the pictures remain hidden from the group members.

5. "Uncover it step by step." - This instructs the leader to gradually reveal the picture instead of showing it all at once.

6. "The other members should ask questions beginning with 'Is he-' or 'Is she-' in the present continuous tense." - This is a guideline for the group members to ask questions about the activity being portrayed in the picture, using the present continuous tense.

7. "Let's begin." - This signals the start of the activity.

8. "Are you finished?" - This is a question directed at the leader to check if everyone has had a chance to take their turn with the pictures.

9. "Let's stop doing the activity. Listen to me." - This indicates the end of the activity and redirects the group's attention to the speaker.

Overall, the expressions used in the activity seem clear and concise, providing clear instructions to both the leader and the group members.