switch from normal to composition scheme

How we can switch from regular scheme of GST to Composition scheme?
 

If I want to switch to composition scheme wef from 1st Apr'18, when should CMP -02 be filled ? Closing stock for the purpose of paymen of ITC should be considered till the date of application in CMP 02 or before that ? Where should the stock details be given for payment of Tax ? Further if I file CMP 02 on 29th March ? what happens to sale n Purchase from 29th Mar till 31st Mar ? Can I charge GST for this period n claim ITC ?

Please guide