How Exactly Is A Follow-On Taken By The Battting Team ?
Not 100% sure of your question. Law 13 deals with the follow-on:
1. Lead on first innings
(a) In a two innings match of 5 days or more, the side which bats first and leads by at least 200 runs shall have the option of requiring the other side to follow their innings.
(b) The same option shall be available in two innings matches of shorter duration with the minimum leads as follows.
(i) 150 runs in a match of 3 or 4 days;
(ii) 100 runs in a 2-day match;
(iii) 75 runs in a 1-day match.
So basically once the team that bats first bowls out the team batting second for at least 200 runs below what they made they have the option of enforcing the follow-on, i.e having them bat a second time. Its important to note that a team does not have to enforce the follow-on, and can chose to bat as they normally would in the 3rd innings of the match.
The captain of the side batting first must inform the other team's captain and the umpires in order to enforce the follow-on.
Hope that answers your question.